Yes 24 hours if the other team waits until the last minute (just before 0:00 UTC) to make a move or almost 48 hours if the other team moves almost immediately (0:01 UTC) when their turn begins and the 24 hour clock does not start until the next 0:00 UTC. The later scenario is unlikely even on move one because it would might sense to wait for new players to show up.

That sounded fair to me. If someone has a better idea I am open to suggestions.

Based on the graphs Taras compiled in the other chess thread it seems that more people tend to join as the game continues. How that should impact the time limit I am not sure but I know it makes counting votes more tedious.