At 5 months, my older DS had two naps a day. If I were you, I would move the first nap to 10:00 am and the second nap to about 2pm. Then I would also make bedtime earlier, like 7 or 7:30. I know when I went to 7pm for DS1 he began sleeping 12 hours at night consistently. (both of his naps were about 1.5 hrs or so)
Good luck!