Agreed. We can't give you a time because it depends on how much you're enlarging and cropping, how dense the negative is, what type of paper and developer you're using (and what developer dilution), the temperature of your darkroom, the phase of the moon, how many children you have, and how the Saskatchewan Roughriders are doing.
Okay, the last three maybe don't matter.
Test strips are the way to go.
I typically have the enlarger lens at f/8 (most lenses are sharpest around there) and my exposures are typically in the 4 to 60-second range depending on whether I'm making tiny prints or quite large ones. A test strip will help you figure out what you need.