Inspired by this answer and the comment by @jgn, it made me dig deeper into the wording of the Geas spell, and how it doesn't seem to tell you if you can only give commands at the beginning, delay the command for another time, or even continue giving additional/new commands. The beginning sentence seems to hint at a single command (emphasis mine on the singular nature of the wording):
You place a magical command on a creature that you can see within range, forcing it to carry out some service or refrain from some action or course of activity as you decide.
And also later:
You can issue any command you choose...
But in the middle when explaining what happens when it ignores you:
...it takes 5d10 psychic damage each time it acts in a manner directly counter to your instructions...
which could have easily been made singular if it was a single command.
this answer to a different Geas question seems to say that it's a singular command, but it's not backed up by anything, and doesn't say when you can issue the command.
So my question is: When do you / can you decide what command(s) the affected creature should follow?