The right amount of practise is hard to quantify; however, the more practise you do the better you will get. Just think about all the time you spend watching rubbish on TV! This is perfect drum practise time! I tend to practise more at the weekend when I have more time. During the week I work on improving my rudiments and maybe try out ideas that I've found or have come up with myself. The truth is, if you put in 15 minutes a day you will improve. If you put in 30 minutes a day, you will improve more... and so on. Those aiming to progress rapidly should put in 2-4 hours every day. Try and develop a routine. Here's one I've made up which you might like to try:
Feel free to come up with your own and don't expect to see results immediately!
Here are some really useful websites:
40 Essential Snare Drum Rudiments - This site by Vic Firth allows you to hear the patterns and watch movies of them being played.
PAS International Drum Rudiments - This site contains those rudiments deemed important by the Percussive Arts Society... the ones that REALLY count!!!
If you play an acoustic kit and don't want to bother the neighbours, it's well worth investing in some drum silencer pads. I currently use a combination of RudiMat and QT pads:
RudiMat Review - "Drumming is often about compromise. Many drummers must practice at certain neighbour-friendly times or in set places. Even if you can play at home, silencer pads are never quite the same as playing the real deal. With this in mind specialist rubber and foam company Coplan Ltd. have created a the RudiMat silencer set that deals with these issues".
RudiMat Drum Kit Silencers - Here's the place to order them.
QT Kit Silencers - These are also very good silencers.