You shouldn't be choosing a starting hand because it's been X amount of time since the last time you played a hand. The primary goal in poker is to win chips. You achieve this goal by:
- Identifying your opponents strategy.
- Determine, and implement, the maximally exploitative response.
So, before you even sit down at a table, whether it's online or live, you should have, at the minimum, a readless starting hand range that will maximally exploit the strategies of the average population. That's a pretty complex task but you can, once you understand the general idea, come up with a rough starting hand range that will do well versus the population.
This is an iterative process. As you gain more information, solid or intuitive, on the population you can tweak your readless starting hand ranges accordingly. Your best bet is to sit down with a tool like Pokerstove or Equilab and craft some starting hand ranges that you think are reasonable.
Then, once you have said range, it's no longer about how long since you've last played a hand. You know which hands you're playing and you're playing them every time you get them. At least, that is, until you gain reads on the opponents at the table. At that point, you should adjust your readless strategy accordingly to maximally exploit their playing styles.