6-7 hours per day!?? o.O
You can precautionarily replace strings as frequently as you like, and can afford.
[br]Other than the cheapest rubbish strings or some other issue with (usually the saddle) of your guitar, you won't generally break strings unless you're doing a lot of bending, the strings get very worn, or your attack is gorillaesque.
That said, there's always a risk you can break a string. Even near new. One day you will. Usually E or B strings. Goes with the territory, especially electrics with their common lighter .9 & .10 gauges and often heavier picked Rock/Metal attack.
Buy a spare couple of sets which you should have with your kit in any case, and then play them until they break or wear out, whichever occurs first. You'll know when the latter happens as [u]the high strings will sound dead[/u] and will start to cause all sorts of tonal problems.
If your current strings are still holding tune, sound OK and aren't corroded to the touch, I'd just play them until they break or start to illustrate they worn out.