When are the contributins on an owner required to be made. The case at point is a sole proprietor. He does not have a set salary to withold contributins from. Can he elct a contributoin st yearend?

Yes. The sole proprietor may make his elections at year-end

With the election in place before year end, the contribution is due before the due date of the return, but should be made sooner if the EI is capable of being determined any sooner.

See, e.g., Treas. Reg. Secs 1.401(k)-2(a)(4)(ii) and 1.401(k)-1(a)(6)(ii)(B).