Hi Max,
I have heard that rumour or theory too, but don't know if it makes much difference really. There's also a rumour that zapping when the pet is starving increases the chances of a good zap.
All the pets I'm zapping are happy and bloated so if you watched their results for a while that might give an indication.
One thing I think might help is zapping your pet as late in the day as possible, go by neopian time and try to zap in the evening or late afternoon. Remember though the lab ray is "evil" and you'll always get zaps when it lowers stats etc.
When I first got the lab ray it was over 6 weeks before I got a colour change. Good luck with zapping. It's not unusual for the lab ray to lower stats for several days in a row.
Are you zapping mainly for stats ? or for colour changes as well ?
Yeah I agree about the training school, I use a combination of coltzan's shrine and the lab. Most annoying thing about the lab is it does seem to lower defence quite often.
btw the name is Silva. :)