I think we're getting my daughter a tablet for Christmas, but I can't trust her or her mum to keep an eye on how long is spent on it.

I'd prefer not to get an Amazon fire tablet, I'd like Google Play on the tablet without any fuss. I'm not sure where to grab a Hudl not that they're discontinued.

Any third party apps that are in anyway decent in restricting time on a tablet?

Kids place has a timer and you can also control which apps can be accessed from the tablet.

You might like to consider using a router based solution

https://www.opendns.com/home-internet-security/

With this, it is much more difficult for young children to get round constraints. You lock down what content can get through the router (and password protect it so the 'little monkeys' cannot alter settings).

No system is totally foolproof but if children get enough knowledge to get round a router based solution, then your 'battle' is lost, and you can at least be proud of how clever the children are.

Of course, ultimately the best protection is education and trust ie taking time to explain to children dangers of internet eg grooming, viruses etc. Most children are taught and accept you should never get in a car with strangers. Same applies here.

You may have bought one already, but Argos are doing an 8 inch Lenovo tablet for £49.