Attendance requirement works out at about 6 weekends per year minimum, but you will find that your Sqn/Coy will have training on at least once a month if not more. It will be up to you how much you do. If you are keen and have plenty of time (no wife, girlfriend, friends, job etc) then you could do almost every weekend and courses during the week, but if you are normal then it will probably work out at around 45 days per year.
Ultimately if you enjoy the TA, you will probably want to do more and get ahead, which will require a greater commitment on your part. However initially, I would work on the one w/e per month, one evening per week and two weeks annual camp each year.
But don't forget your priorities Family -> Work -> TA. If you can't fit it all in, drop the TA.