AO: I never had the patience to do it properly until last year. That took me... 3-5 weeks. I really don't know because I only vaguely remember it.
AE: I've never done it completely right, but I got the good ending in... something like 4-6 weeks. I don't remember this much better.
MO: Not all that long. I bet it was something like as long a AE. Only because I ended up doing lots of it again because it was very fun at the time.
SW: What was it... A month or two? I don't know. Very hard and very fun.
All in all, every Oddworld game put together took something like 3 or 4 months.