Thanks everyone. I let them have 3 hours and they were fine. It's a sun trap on the decking and even with the blanket, I wasn't sure whether they'd be too hot. Luckily I work from home so they can have plenty of run time because they only have a 120cm cage, which I thought would be ok for them before I adopted them. I didn't realise how big they were and now I'm feeling guilty, especially after seeing all the fantastic set ups on here.