I've found I don't have as much trouble with SPs lately (at least for the first round) as I have in the past, sometimes even if masturbating fairly regularly. It more depends on the woman, the atmosphere, how she looks/feels/sounds/moves with me, etc. I do notice that I'll start to reach the point of orgasm and if I try NOT to cum (since it feels too early or whatever), it'll be MUCH longer before I reach that point again (and maybe not within the time of the appointment). So often I'll just let it go and enjoy the moment and if we go a second time, awesome. If not, well, it may still be a great appointment. (it always feels great TRYING, right? lol!)
I've found diet can also be an issue - I noticed Red Bull beforehand means I take MUCH longer to cum, sometimes not at all.
Take a look at some of the basics of good living: healthy foods, plenty of water/healthy fluids, plenty of exercise, good sleep (this is also one of my challenges due to work/life stresses).