I don't have much experience on changing match time but would like to try to answer.

Quote Originally Posted by Tyltyl View Post
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1) I never needed to postpone a match before, but this time I have 2 important matches in one day: a Cup's quarter final against a higher level team and a league match against my runner up. So I would like to play the league match before the cup match so I can max out the condition and then play both matches. I don't understand the following image. It starts from 4:30 and ends to 2:00, does it mean that I can schedule a game at 4:30 in the morning before the original schedule (10:53 AM), right? I can't seem to play in the afternoon, but I can play at 00 or 01. Does it mean 00 and 01 the day after the original schedule or before?
Yes for all questions as I understand.

Quote Originally Posted by Tyltyl View Post
And also, I don't plan to play in the afternoon of course, but why doesn't the game let me play in those specific PM hours after 13 if my next game is at 21:17, several hours after?
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These hours are not available for your teams or your opponents' team. Your opponent likely will have another match at 16:xx of your time zone. So it will not be available from 13:xx to 19:xx. As your team have a match at 21:17, your team is not available from 18:17 to 00:17.

As I know, matches can only be re-scheduled on same season day, cannot be rescheduled within daily maintenance hours, should be re-scheduled to 24 hours later or more, and should not be arranged within 3 hours from other matches of your team or your opponent.