How can I push back LO's bedtime?

I haven't followed any type of schedule w/ds really.  I feed him when he's fussy and rooting around and bounce him to sleep if he's acting tired (he's a major sleep fighter) their is no set time between feedings etc.  Sometimes he naps during the day, other times he's awake most of the day.   I breast and formula feed. 

He usually had a witching hour from 8-9 ish and then would fuss a bit after eating and it would take me an hr or two to get him to sleep.  Now he goes to sleep somewhat easily at night (as in this past week) and has been going to sleep around 9-9:30.  He's been sleeping 7-8 hours this past week.   Not sure how long it will last, but I'm keeping my hopes up.  I'd like him to stay up till 10 due to my DH's work schedule.  

He was pretty fussy earlier and so I gave him a bottle and he fell asleep after eating which was at around 8ish.  He use to only sleep for a 1/2 hour max and then wake up, but he was still sleeping an hr later.  I figured I'd wake him up, but I tickled his feet, that did nothing. Picked him up..nothing.   My DH kissed him a bunch and rubbed his back...nothing.  I figured, if he's in that deep of a sleep, I'd better let him be rather than try and force him to wake up.   So, if he sleeps 8 hours, he'll be getting up at 4..I really don't want this 8 hour stretch to be starting so early since he doesn't always go back to sleep after he gets up.

If I want him to stay up till 10 and he falls asleep after an earlier feeding, should I try and wake him up right away and keep him up by playing w/him?  Or should I just leave him do as he wants?