Whee!!! Nainggit ako! I shall have to live what i missed vicariously through your eyes hehe.
It was technically my third time. I was there in 2002, then again in 2004 (but only for a few hours stopover on my way to Hue). I'm sure you could go there anytime. You could finish the city in a day. There are several day trips out of HCMC. You could also opt to exit Vietnam via the Mekong River to Phnom Penh. :)