Kairea- what is too much depends entirely on you, and if you get any hits. for example I ran a 2 minute lyme frq from Newport a couple days ago, and the result was a metal dump that made it hard for me to get out of bed the next day. So it all depends, if you hit a critter like lyme, a few minutes might be too much.
I found that when using contact, having the electric run through me for any more than two hours a day would just leave me tired, so that might be another issue.