DD has been down to 1 sleep from about 9-10 months .
I find i stretch her out in the morning and she goes down after lunch for 3-4 hrs.

I found it was time to go from 2 to 1 when she was not at all tired late at night. so slowly by slowly would fill her mornign with activites and she woul dbe ready for a good sleep in the arvos.
I did the same as PP, Julia used to get up at 7am miss her morning sleep so I would put her to bed straight after lunch. She still goes to bed for her 1 day sleep around 12.30 now and sleeps til 3pm every day. I also put my 5 1/2 month old to sleep at the same time and they sleep together in the same room until the same time its bliss. If I dont put Julia down after lunch for her day sleep she gets really cranky by 5pm. About every fortnight she doesnt have a day sleep for one day then it all goes back to normal.