Switching the coins on/off wouldn't be needed, they'd be available to be mined all the time. Its just that trades would be less frequent (so there is some price risk with holding for 12 hours or something).
Price risk is pretty bad on these coins. They could (and likely will) crash at any time.
The reason I suggest turning them off is there is usually going to be an almost-as-profitable coin the mine that won't incur the price risk. I guess you could program in some kind of profit threshold where you are willing to mine-and-hold (temporarily) if the profitability is sufficiently better.