12 Hours!!!
Joe,
You've got to try and get that down to three or so hours. Reading your post I think you problem is lack of confidence rather than a lack of will, which you clearly have in abundance and that is massively to your credit.
You are using a pre-spray in SPM that is generally accepted as one of the best, so if you sprayed a set of stairs, then hand brushed it in and extracted it, the result is likely to be as good as it gets and that is where I think your problem lies, inexperience mixing with a lack of confidence making you question everything you do and doubtless having you re-clean things that are no better the second time around.
Simon