well im in prelims, and im studying pretty hard. i mean, it's a good habit to develop right - not straying off track and getting disturbed and what not. it's different for everyone, but for me, i have the set mind that if i put in effort and do well this year, i'll be doing a lot better next year, because i've been through the hard times, know what to stress over and what not, how to deal with it, etc. etc. most things won't be new to me.
and as for 3u maths. ...i dont believe you should slack off at all. that is, unless you want to fail.