As an ex CPL/IR instructor, I would definitely advise completing your IR as quickly as possible, due to the reasons mentioned by previous posters. I have come accross guys who have attempted to complete it either part-time or more usually with long breaks in between and the result generally isnt pretty!! ....not to mention the higher costs due to the one-step forward,one-step back scenario.
You dont have to complete it 100% full-time but "weekends only" or "one day a week" aint gonna be in your best interests. There will always be whizz kid pilots who can manage it but i assure you they are in the minority. Remember too thats its a 50/55 hour course so it can take a while to complete..even full-time. Good luck whatever and whereever you choose
Alph