I did haphazard training, spread out for many years. Never could get it to work - by the time I got back in the air I had forgotten all essential stuff. In the end I did one of those 10-day intensive courses they have here in the states (PIC). Although mine was 11-days because I did it on a twin. It was flat out. 4-5hours of flying each day, cramming, theory, sim. I breathed, ate and slept IFR for 11 days straight. And I can tell you I would not be an IR pilot today if I hadn't done that. I have terrible memory, so cramming and making it all fit together in one go was the best solution for me. If you can retain info easily and have the ability to digest, then slower training might work for you. It's all individual.