No it's not normal, it's really bad to be honest but I think you already know that.
Is the mum struggling with the holidays, like having to work whilst having her daughter home or struggling with the cost of things when out and about? And maybe it's just totally spiralled?
Me and a friend were talking about screens and stuff yesterday, our kids area both 4.5 so start school in September but their nursery was school time only so this is our second 6 weeks holiday.
She was saying her son is always on his tablet or playing PS4 games (usually with his dad on the playstation) They've got a 5 month old and are going away this week so trying to get organised for that. I said don't stress too much just maybe use the holiday as like a re-set and go from there if you want him using them less?
My son doesn't have a tablet and we haven't tried him with console games because to be honest we don't think he has the patience for them and it's just another "thing" to have to think about/regulate. But he does watch the telly, mostly iPlayer and some other bits but not YouTube because we're a bit wary of it. He has phases where he's not bothered about watching and others where he'd probably watch all day if we let him. We have found the more he watches, the more he wants it on so we try to be mindful of that and stick to rough times to watch it in between being out and about or in the garden or whatever. It can be hard as ds doesn't like busy places and obviously summer holidays most places are. But we find ways around it. Also, the paddling pool has been a big hit this year.
With the late nights, again it's indisputable that a 5 year old staying up till gone midnight on a tablet is not good. I get being out of routine, knowing they've not got to get up for school etc but there's got to be a limit! My son struggles to wind down and is often up until gone 10pm even though we do no screens after 6pm. The light nights don't help. This summer we've been taking him to the local family friendly pub after tea as they have a playground and a bouncy castle and he happily bounds around there for an hour or more. Sometimes he falls asleep in the car and we can carry him up to bed, other times he'll still be awake, but we just do our normal wind down routine after (supper and books downstairs then bed with an audio book or book) But at least he's had a last hit of fresh air and exercise while the weather is nice and it's a bit of a break for us too!