from 3 months till about 7 months my DS would have a 30-40 minute nap after being awake 2 hours. Repeated this pattern throughout the day.
At 7 months he stretched out his awake time in between naps so he dropped down to 3 naps per day. Still around 45 mins each.
At around 9mo he dropped the late afternoon nap and had just one in the morning and one in the afternoon. At this stage the afternoon nap (finally!) got a bit longer. 90 mins on a good day. Usually an hour.
At 13mo he dropped the morning nap and now just has one nap per day after lunch for 90 mins or so.
My DS had 3 short naps for ages, til about 8/9 months I think. On a bad day they'd all be a max of 30 mins each! But sometime around 9/10 months he started having 2 naps and occasionally 1 long nap. He's 14 months now and still gets very tired about 3-4 hours after getting up, usually sleeps for 40-50 mins, and then has an afternoon nap of about the same length, or occasionally will have one long nap of over 2 hours. Sorry about that - no useful pattern!
My 6.5 mo DS has 3 naps - each one typically about 2 hours after the start of a milk feed e.g. around 9am, around 12pm, around 4pm. Unless we're out and about in the morning and he's really tired, the 12pm nap is short e.g. 30 minutes and there is the small chance that he will need a fourth nap between 12pm and 4pm to make up. The 9am nap is easiest - no battles, out like a light! I got so demoralised the day he didn't have that 9am nap recently after a long battle - but luckily that was a blip (that nap is essential for me as that's when I get to have a shower and some brekkie!).