2000-2001 iirc. The local cartoon network showed a portion of the Boo arc on repeat during that timespan, and for some reason never showed the rest. Got hooked on it back then though, and came back to it in Grade 4 to watch the whole series. So really since 2004ish.
It started on toonami in 98. It was on Fox saturday mornings at like a ridiculous hour (6am?) in 96. My friend actually convinced me to get up that early to watch it.
Then it was '98ish. I definitely remember it being one of the Raditz episodes in the evening after I got out of school or daycare or whatever the fuck it was.