Agreed the run time rule is not very clearly defined.

I'd suggest setting an explicit run time and hardware - say a maximum of three hours on, ooh I dunno, a 2.8Ghz Celeron

If you only propose challenges which would reasonably be expected to complete in seconds or minutes a restricted time limit is not going to be onerous.

Sure, it will mean that some methods cannot be used, but that's part of the challenge - if you try a tricky shot off the fairway over the trees and you land in the lake then you have to accept a dropped shot and try another way around.