How much screen time is actually ok?

My kids are 6 and 9. They want to be on tablets or switch all the time. We do maybe 1-2 hours on weekends and some during the week if weather is bad. My wife thinks thats too much, I think its reasonable. The 9 year old wants to get into gaming which part of me gets but Im worried about the addiction thing. What does everyone else do? Are there kids who can actually moderate or is it just a constant battle?