IMO 13 months is a tad early to go down to 1 nap but it isn't unheard of.
My 16 month old has been on one nap for about a month now, maybe 3 weeks. She sleeps from about 7-7. Sometimes she goes down earlier though depending on what time her nap is. Hell, sometimes she goes to bed at 6:30pm!
I would try pushing that morning nap up by like 15 minutes every week or so until it's closer to lunch time. Then maybe move the bedtime a little earlier. I personally wouldn't put my DD down for a nap that late. I'd rather just put her to bed earlier. Just adjust slowly so that your LO isn't overly tired.
My 13 month old son sleeps 7pm to 6:30am. Naps 2x/day at 9am-11am and 2:30pm-4pm. He just loves to sleep! I know at some point I will have to cut out a nap but he's happy with his sleep schedule.
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