# How quick is the transition from one concentration spell to another? [duplicate]

While it's been established that concentration spells can't overlap (When exactly does a concentration spell end from casting another one?) this brings up the nitpicky question of 'how long is the gap between one concentration spell ending and the other beginning?

## Example:

I cast Darkness on myself and that spell completely obscures me from sight for as long as I concentrate on it.

Darkness:

Magical darkness spreads from a point you choose within range to fill a 15-foot-radius sphere for the duration. The darkness spreads around corners. A creature with darkvision can't see through this darkness, and nonmagical light can't illuminate it.

While I'm concentrating on the darkness spell, I cast Invisibility

A creature you touch becomes invisible until the spell ends. Anything the target is wearing or carrying is invisible as long as it is on the target’s person. The spell ends for a target that attacks or casts a spell.

So now I'm invisible.

It's well established that the spell effects from concentration spells can't overlap, so the darkness spell ends when I start concentrating on Invisibility.

But nothing mentions the amount of time that passes between each.

## The Problem:

Say I'm trying to hide my identity, or otherwise pull a "mysterious force" scam and I don't want my opponents to see me at all.

Does the Darkness end when I start casting the Invisibility spell?
(in which case I'm visible, briefly, while the invisibility spell is cast)

Or does the darkness end as soon as the invisibility takes effect?
(So I never actually become visible?)

And to be clear, I'm not asking about the converse (First cast Invisibility, then cast Darkness) because the act of casting any spell would end the Invisibility, and that strikes me as a potentially different case with potentially different rules in play.

And this seems different from the combat use case mentioned in the previous question; the spells don't overlap, and the amount of time they don't overlap doesn't matter in game mechanics. But in the case, it actually does matter because of what my opponents do, or do not, see.

Covered in RAW/Sage Advice/Etc. anywhere, or is this down to GM's discretion?