I did mine at weekends also. Didn't find any real problems doing it that way. Ended up doing about 90 minutes over the minimum.
The biggest problem was that clocking up 50-odd hours only at weekends simply takes quite a long time. I was also doing mine during the winter in a non-deiced aircraft, so inevitably there were quite a few cancelled lessons. By the time I'd finished my instructor was sick of the sight of me.