Dropping down to 1 nap

I’m sorry if this has been asked a million times already. When did you decide to drop down to 1 nap a day?

My son has been taking 2 naps and lately they have been long, like 1.5-2 hours each. But he’s been waking up once at night and hard to settle down. Likely teething. And of course he’s fighting me on the naps and sleep too. At night he sleep about 9-10 hours.

TIA!