After blotting their copybook with their crash in Imola a fortnight ago, Russell and Bottas bounced back superbly in qualifying for the Portuguese Grand Prix.
But asked by GPFans Global as to what it will come down to, that he does not know already about either driver that will help him determine who should land the seat, Wolff replied: "I hope one day I wake up and it becomes clear.
"I think we need to look into the season, how the next races unfold, and then it is a judgment call, I believe. Not a very scientific response, but I haven't got any at the moment."
Wolff has stated this year that it is his intention to confirm his driver line-up by as early as the August break after being stung last year by the delay in the negotiations with Hamilton that did not start in earnest until after Christmas.
The seven-time F1 champion finally put pen to paper on a one-year deal in January.
Wolff has confirmed that no new negotiations have yet started with Hamilton, but that early discussions have at least commenced, and the signs are encouraging.
"I wouldn't say we have gone back and forth but at least we have learned our lesson that we wouldn't leave it until the Christmas holidays," added Wolff. "That was definitely taking it too far.
"We are in a very good place, our relationship is growing stronger, like every year, and it's about time to give it a little nudge and start to speak, and this is what we are going to do soon."