This is my 3.5 hr EASY
7 am - Eat
7:30 - 8:15 Activity
8:30 - Sleep
10:30 - Eat
11:00 - 11:45 - Activity
12:00 - Sleep
2:00 - Eat
2:30 - 3:15 - Activity
3:30 - Sleep
5 or 5:30 - Eat
At this point I try to get him down for a catnap sometime between 5:30 and 6:00 - usually just a walk in the stroller for about 30 minutes
7 or 7:30 - Eat
7:30 or 8:00 - bed
Sometimes his naps are 45 minutes, other times they are between 1 and 2 hours. If he wakes early and I can't get him back to sleep, I just try to keep his activity time to 1.5 hours and put him down a little earlier after a feed. he never take three 2 hour naps during the day. Like yesterday he napped for 2 hours, then 1.5 hours, then 1 hour, so I just worked around that.
It varies how long your lo will take 45 minute naps. I too am afraid he will get used to it, but he doesn't take ALL 45 minutes naps (thankfully). He may have 2 days where he will nap only 45 minutes, then the next couple of days the naps are longer, so I know he is able to take longer naps. If you think the naps might be a problem, you could always try wake to sleep.
Babies spend the first couple of months sorting out their nighttime sleep then move on to work out their day time sleep (hence the 45 minute nap monster at this age). I am told that it usually works itself out, but that could take a couple of months. I know this is probably not what you want to hear, but again, if it becoming a HUGE issue, you can always do shh/pat or wake to sleep to try and extend the naps!
HTH