Screen time has gotten out of hand and I don't know how to rein it in

During the school week my kids were using their tablets maybe an hour a day but over spring break it ballooned to like 6 hours easy. Now that school started again they don't want to give them up. I feel like I completely lost control. How do other people actually enforce limits? Every time I try to take the devices away it's a complete meltdown and honestly I'm too tired to deal with the battle.