for me it depends weather im on top or bottom..
on top i usualy never finish no matter how long im up there, i just do my thing till shes happy then i make em jump on top for 10-15min and im golden
Or just honest. SSRI's (i.e., Zoloft) can help premature ejaculation. 40% of men suffer from this, and the average penetration-to-ejaculation time is only 1:45 seconds in those who suffer from PE.
I would suggest Kegel exercises first. If that does not help, then talk to your doc about an SSRI. They can significantly delay ejaculation. (In fact, some men become anorgasmic while on an SSRI and must stop the drug in order to start ejaculating again.)