0-3 shares per day is just fine. The shares are active for a day and a half, so almost every single day you will have one or more shares working. Your daily earnings will fluctuate but only rarely to zero and over relatively few days it will average out.

With a much lower hash rate like 10 GH you could make the argument it will take much longer to average out, although I still maintain at that point the numbers are so small the variance doesn't matter. If you get $0 instead of $1 on one day and get $2 instead of $1 on another day you're not going to go bankrupt over it.