Nope. It's not that. That function works differently. That is unique for each team you are trying to inv for a friendly match. For instance, let's say I try to challenge you to a friendly right now (08:00 GMT). If you have a match soon (let's say 09:00), I won't be able to set the time to any sooner than 12:00. But I can challenge another player who doesn't have a match within the next 3 hours.

Last night it was the same message no matter who I tried to inv to a friendly so I trained the squad instead :<