Day/Night Temperature Differential for Seedlings

My beans popped yesterday/early this a.m. Indica Dom Purple Penny fr ProV.

Now that they are up, should I take the heat mat out of the dome ?

How important is day/night temperature differential for young seedlings ?

When should I start a fan ?

I start my fan once the cotledons are up and running, I like the temp of my mat at 25c/77f 24/7
at least until the main leaves take over

The heat is fine it's the dampness you need to worry about, don't overwater and only water when pot feels light, root fungus (root rot) is the number one killer of seedlings. I'd leave the dome off for extended periods as well.