Psims,
There are some pretty pessimistic estimates out there. I can only remember about four cancellations during my training. However it was back in the days when we thought the world was still cooling down!
I started in February and completed the course in September. One lesson each Sunday and sometimes one midweek in the summer. Total 43 hours. I did have only one instructor and he was happy to vary the lesson to suit the weather. I probably did more than the required 3 hours instrument appreciation and some lessons were VMC on top. Dundee was a great place to learn and I never once had a cancellation due to an aircraft going tech or instructor being unavailable.
There are guys here who have frozen ATPLs and an instructor ratings gained within two years acheived at weekends.
You need a bit of luck, a professionally run school but mostly determination.
DO.