To be honest for the stock market, I only buy when at least 1 line below the average, and I'm selling 1 line above the average, which is probably as far as the prices fluctuate.

For Tier 1, That would make a ~14% increase. (5 minute CD)
For Tier 2, That would make a ~30% increase. (15 minute CD)
For Tier 3, That would make a ~62% increase. (30 minute CD ? 45 minute ?)

If we take into account the cooldown, it's almost always worth it to use only the lower level stock market, even if it means a lot more of active time. Using the higher tiers would be good only if yo'ure planning on idling for a long time / going offline.

EDIT : And I've just realised that I said almost the exact same thing than above x)