I need a safe space because they're really pissing me off on Twitter

If it's a situation in which they're the only person who can do it/has access to whatever you need, then you have to ride their ass about it until they do it.

I've personally never given someone a date then just completely ignored it, but I have been in the middle of a commission before when something happens in my personal life and kinda fucks everything up. If it's that situation then let them know if they can't do it for whatever reason that it's okay