Matches are scheduled to dates during the season. In the league you e.g. play 2 matches per day. Typically one home match and one away match.

The home team has 12 hours to kick off matches on the day they get "released" for kick off. The 12 hours start from 8AM CET (Central European Time).

You will see the text "Play match before X time" on your next match page when  you are the home team and matches are reseved for you as the home team to kick them off.

When the 12 hours has passed, after 8PM CET, and "Play match before X time" reaches 0 both manager can kick off the match.

If you are the away team and the match is not released so both managers can kick off the match yet you will see "Waiting for opponent to kick off the match".

So basically the home team can kick off the matches. If the home team does not kick off the match in time both teams can start the match the day after it is scheduled after 8 PM CET. 

So always make sure you play your home matches as you get an advantage when being the team who kicks off the match.

If matches are not played at midnight CET (16 hours after home team can make kick off) they will quite often be started automatically to make sure the tournaments can run smooth.