As for the original question, I agree with those who say that the tlhoS in tlhoS wa' ben qaSpu' wanI' incorrectly tries to apply itself to the noun phrase wa' ben. I like mayqel's solution of wa' ben HochHom qaSpu' wanI': simple and accurate, though I feel a little uncomfortable about having "most of" a particular moment in time. I wonder if one could say wa' HochHom almost one as in wa' HochHom ben qaSpu' wanI'. I wouldn't feel comfortable using that either, but it does seem to follow all the rules.

Imprecise time expressions are always a challenge.