This year I am applying for the BEd at the RSAMD, the BMus at Glasgow Uni, and the BAAM at Strathclyde Uni. The auditons are coming up in Jan/ Feb.

I'm really inexperienced at audition, so I would appreciate any advice on how much preparation (i.e. practice) I should be doing for them.

I sat Grade 8 last month, in the run up for which I was doing four hours a day. However, since then, I have only been averaging two hours.

I only need a programme of ten minutes for my auditions, and it is unlikely scales/appregios will be asked at all.

Am I doing enough?

In all honesty, you might be better off asking your teacher that question. Without actually hearing you play it's difficult to say how much time you should be spending practicing.

I gather the degree with be 50/50 academic/performance and that the minimum standard they will have asked for at entry is Grade 8. Have you prepared new pieces for the auditions, or are you playing music you already know (works you played for the exam)? Whatever you have chosen, you need to be at the point where you are refining your performance of them, rather than still learning them.

It would be wrong to assume they definitely won't ask for scales and arpeggios. At an entrance audition you need to be prepared for any eventuality.

Amanda has basically said what I would have said, definitely do not rule out the practice of scles and arpeggios, I'm in first year and practicing them for an hour each day as awarm up, followed by an hour of feulliard but that's just me, if you've just done grade 8 I would say an hour to an hour and a half a day would do you good for general everyday practice, but for auditions I would try and fit in 2 - 3 hours. You definitely want to nail your pieces/scales/whatever else in the auditions, so structured practice in small quantities at a time (i.e. 30 - 45 minutes at a time with half hour/one hour intervals) is the best way to approach it. You don't want to be doing 4 hours at a time with no rest, which I found out was a bad idea when I did it the day before my RNCM audition (i didn't get in, surprise surprise )
Of course you're applyingto different courses at different places, so the amount of practice you do during the course will depend on which course you do. So if you're doing the BEd course, then the amount of practice you do won't be as mch as if you were doing BMus, because a lot of us Academy BMus folk in Glasgow practice 3, 4 or even 5 hours a day. Some of the pianists even manage 6, but they're just loners haha, no offence intended if anyone out there is a pianist.
In general I would say do as much practice as you have time for, I usually go in at 8am and fit in an hour before my first lecture, then after an hour or 2 of rest/sleep in lectures, I do another hour before lunch. It can be pretty spread out and structured around your lectures, most people practice in any free hours that they have