I'm trying to understand how the Feywild time warp effect works. (Note that use of wish spells, or any other effect that alters the time warp effect for only particular creatures, are out of scope of this analysis.)
To establish the scenario, suppose that at a given time, an adventurer in the Material Plane stands near a portal to the Feywild, takes two synchronized clocks both set to zero, and puts one of them into the Feywild.
Suppose clocks can count days and "time zero" is the time the clocks were synchronized. We call the clock in the Material Plane the M-clock and the clock in the Feywild the F-clock. So we write e.g.:
M/x = the time that the M-clock reads x days
F/y = the time that the F-clock reads y days
There are two models that seem to be suggested by the text, neither of which makes complete sense.
The Monotonic Function Model
The text says that time passes at different rates in the Feywild and Material Plane, and that this ratio of time rates can change. Thus, one can consider what would happen if someone was standing by the M-clock, looking into the Feywild at the F-clock, and repeatedly recording the time shown by the F-clock e.g. every second on the M-clock. Since time does not go backward on either plane (just forward at different rates) this would yield a monotonically increasing function f(x) that gives the time on the F-clock when the M-clock reads x. (And f(x) would presumably be generated by some random process - whatever makes the time run at different rates)
In that case a user who left the Material Plane at time M/x would arrive in the Feywild at time F/f(x). Similarly, a user who left the Feywild at time F/y would arrive in the Material Plane at time M/g(x) where g() is the inverse of f().
This interpretation leaves it unambiguous as to when a person leaving at any given time will end up. It also makes it impossible to send messages back in time (i.e. from F/t to F/w, or M/t to M/w, where w < t) and so does not allow for time paradoxes. However, it is not consistent with the way the effect is described in the rules:
First, consider the case where Alice goes from the Material Plane to the Feywild at time M/0 (and thus arrive at time F/0), then at time F/2 Alice jumps back to the Material Plane. The probability that Alice will arrive back at M/730 is 0.05 (if she rolls a 20 - days into years - on the time warp die). However, suppose instead that at time F/1 she jumped back to the Material Plane for a very short time (let's say a fraction of a second) and back to the Feywild, then stays in the Feywild until time F/2. Then this is two separate trips and in order for Alice to arrive at M/730, she would have to roll a 20 both times, a much lower probability. But this makes no sense since f() is a global function that just represents which M-clock times connect to which F-clock times, and doesn't depend at all on when Alice made her jumps.
Thus, if this were the case then either (a) the distribution of the ratio [Material Plane time interval] / [Feywild time interval] given a randomly selected interval in Feywild time [w, t] (that is, (g(t)-g(w)) / (t-w)) would depend on the length of the interval. Similarly, this ratio for a given trip would be correlated with the ratio for other trips that took place including the same times. But none of this is stated to happen in the rules.
An interesting concept in this case is that the distribution of time ratios would depend on which plane you started from. For instance, suppose that f(x) was piecewise linear over 0 < x < 500, where f(0)=0, f(1)=400, and f(500)=500. Then, an observer in the Material Plane who selects a random time uniformly distributed on the M-clock to cross over would almost certainly (99.8% chance) find themselves at a time where the Feywild ran faster (100 Feywild days = 499 Material Plane days). However, someone from the Feywild who selected a random time uniformly distributed on the F-clock to cross over would have an 80% chance of picking a time when the Material Plane ran faster (1 Material Plane day = 400 Feywild days)
The Rules-As-Written Model
Given that the monotonic function model appears to contradict the rules, one can instead work the opposite direction, and consider the rules as written, where the time rates are rolled for each traveling party separately.
Suppose now that Alice and Bob, members of separate parties, both go through the portal at time M/0 and arrive at time F/0. Then Alice stays until F/1 and goes back, and rolls a "no change" on the die so arrives back at M/1. Bob stays until F/1440 and rolls a "days into minutes" result, so arrives back at M/1.
The question here is: If Charlie, who was not involved in either previous trip, goes through the portal at M/1, when on the F-clock will he end up?
The rules do not specify, but it seems that any answer below F/1440 will lead to a situation where backward-in-time communication is possible: Bob takes the message from F/1440 back to M/1 and gives it to Charlie to take back to a previous F-clock time.
One could avoid backward-in-time paradoxes by saying that when you leave the Material Plane at time M/x you always arrive at time F/(1440*x), and then when you leave the plane at time F/(1440*x + y) then you arrive back at M/(x + y*z) where z is the rolled ratio. But this would mean that if I was in the Feywild for a few days, and popped back into the Material Plane for a few seconds, I would almost always get back in the Feywild many Feywild-years later, which doesn't make sense.
It is notable that the rules say that the time warp effect only applied in one direction (when returning from the Feywild) Thus, one could interpret this one of the following ways:
When you go from the Material Plane at M/x to the Feywild, you always end up at F/x. This allows for sending information back in M-clock time as well as F-clock time (e.g. have Charlie go from M/10 to F/10, give the information to Alice, then let Alice hang onto it to bring it back from F/24 to M/1). Note that this requires preplanning to send Alice in earlier as well as having to hope for luck that she rolls a result that sends her back.
If I return from the Feywild and wait n days in the Material Plane, when I go back to the Feywild I will always be n Feywild-days after I left Feywild. In other words, if I return from F/y to M/x, then if I go back through the portal at M/x+n I will arrive at F/y+n. Note that this effectively means that each traveler (or group of travelers) has a separate "time offset" - in the above example, after Alice and Bob's trips, if Alice were to go back through at M/5 she would arrive at F/5, but if Bob were to go back through at M/5 he would arrive at F/28. In this case, if one had a network of several people that made several trips to generate different offsets, they could send messages back in M-clock time by having someone with a smaller offset leave a message in the Feywild and someone with a larger offset bring it back.
Is there any RAW or statements from the designers to support which of these is the intended interpretation?
Is there any official D+D fiction or setting material that describes the time warp effect in more detail?