Harvs - might help to look at it from a total sleep per 24 hours perspective. At 2.5 your DS probably needs 12-13 hours per sleep per day. Try and find your DS's magic number.
If it's 12.5 hours... If Ds wakes at 7am and has 1 hour day nap then your DS won't be going to sleep until at least 7:30pm. If you have a consistent wake time, and you know how much sleep your DS needs, then you can fiddle with the length of the day nap to get the bedtime you want.