DD was aboutr 13-14 months and she dropped her 2nd nap! Which totally confused me at the time as she'd been:
Up at 7.30am
Nap at 11am
Nap at 3pm
Bed at 7.30pm

So it was crazy at first as i'd get her up, give her breakfast and then put her back to bed! LOL.

But she slowly began to shuffle the nap later and later and now (25months) she does:
Up at 8am
Lunch at 12pm
Nap at 1pm (75-120mins depending)
Bed at 8pm

Don't worry too much about it. If she took one nap, rejected the second and then got grumpy i just put her to bed earlier in the evening.

HTH