It's dependent on the SG of your starter and what type of yeast. However, in any case...
You'll be actively fermenting but your cell count won't be as high as you were aiming for. If you pitch your entire starter, you'll be better off than if you'd just pitched the smack pack or vial.
If you can wait another day, you'll be better off, but it sounds like you can't. I think you'll be fine since you're gonna have actively fermenting yeast, but a little different/off from expectations.
RDWHAHB, you'll be good. BTW, I have a friend who pitches a single smack pack (w/o starter) and is happy with his brews while being ridiculously anal about water chemistry and types of grains. So, to each his own, I guess. On brews we've done together, I've had to insist on using more yeast, sometimes to no avail.