Is this a ok setting on a 20 slots server when i have permission for reserved slot from 10 hours playtime:

{
"Always allow admin to connect (true/false)": true,
"Always use reserved slot if player has permission (true/false)": true,
"Dynamic slots based on players with permission (true/false)": false,
"Kick other players for players with permission (true/false)": true,
"Number of slots to reserve (if dynamic slots not enabled)": 1
}

That configuration would give you 1 reserved slot, but always allow admin to connect regardless of slots or permission.

But it kicks a player with less than 10 hours playtime, if 2 players with that permission (10h) want to join?

This plugin doesn't have any playtime integration, so that'd be a question for whatever plugin you are using for that.