I would, easier to do it now rather than take the risk of them growing through new turf and then having to deal with them, especially when we don't know what they are. Some weeds will grow from the smallest fragment of root left behind after preparing the ground.

If they are perennial weeds like dandelions, nettles etc then either dig them out or spray with an herbicide such as Round up. This will kill the roots off. It takes about 2 weeks to work properly. But make sure that it is Glyphosate based and will not leave a residue in the soil as this would then kill off your turf.