Since this enlarger is new to you, the first thing I would check is to make sure you have the right bulb. Also double check that your lens doesn't have a lever to open it up for focusing and if it was open rather than stopped down.
For a 5x7 from 35mm, I'm fairly sure I use f16 to get times I can use and that still just gets me around 8-10 seconds. I know the old rule about always stopping down two stops from fully open, but I consider that to be bordering on BS, depending on the lens (I have Componon S lenses and they certainly don't suck). If you shouldn't ever ever ever use the other apertures, they wouldn't be there.