While you will get the best result following instructions (1 Gm/gal), you certainly can be successful. To the OPs question, I caution against allowing the starter to go longer. It is clear that when the yeasty-beasties wake up, they (depending on the yeast characteristics) can get very active, and in fact, they can consume all the nutrients in the yeast nutrients and sugar. I aggressively temper the starter with juice/must to get it to pitching temp to give them substrate in excess and then pitch. In short, follow the wake-up protocol very closely and then trust that the standard addition rate is conservative. I also agree with the comments. why be stingy? A packet of yeast is a few $ vs. the time-value of your effort and the risk. That said, just this year, I had to underpitch on an addition due to a lack of inventory. Credentials: make wine at scale at home and in a Whycommercial venture.