I'm doing a particle physics-based PhD at a british university and have returned a few weeks earlier than my official start date to get familiarised with what I'll be doing. I've been treating it as a 9-5 job, and doing little bits of reading etc. on nights and at the weekend. I've heard all sorts about PhD's being a gruelling battle but right now it seems very manageable, it's not stressing me out at all. Am I devoting enough time to this or can I expect to have to kick it up a gear at some point?