My work involves validating the listing if the company isn't already listed, getting regular citations, reviews, optimized photo's, descriptions etc. After 2 months then i do you-tube videos etc, all this is ongoing so once you get a higher place you stay there!
I never promise to get to the top of Google Places (although we have done on many occasions), but we usually see an upward movement after 2 months, again depending on the competition.
Also i have clients who have 4 or more places listings, so i then do a sliding scale charge.
If you are interested and want to outsource your workload please let me know asap, as i can only do so many listings, as you can imagine it is very time consuming and i always give my customers 100%.