I don't know if this will help any of you but I have been keeping a sleeping log for my DS for a few weeks now in the hope that I can spot any patterns relating to his 45 minute naps and also his night wakings. Some nights he sleeps without a sound all night and other nights he'll wake several times. Well, our day usually starts about 6.30-7 and bedtime is between 7 & 8. Depending on his naps in the daytime his last catnap is somewhere between 4.30 and 6. I secretly preferred it if it was nearer to 6 because this meant bedtime was a little later and he might then sleep until at least 7am! Well, he but does but what I also learnt was that when his catnap was late, we had more night wakings! If he wakes from this nap before 6, we usually have a good night but if its after then we have more wakings so the later wake-up time in the morning doesn't really make much difference because I've had a rubbish nights sleep.
It also leads to a bad night if he has had a very short nap (15-20 mins) in the car somewhere too, espcially if its late afternoon. Now I know what I need to try to avoid although it isn't always possible of course but I'm glad I learnt something. Hope it might help some of you too.