I once tickled my ex girlfriend nonstop for around 20-30 minutes......of course she'd verbally mock me during brief pauses like "Is that all you got?!?" (yeah she was cool...LOL)
Little over an hour, the only breaks were long enough for me to move from her upper to lower body and vice versa. She was exhausted, but in her words: "the orgasm at the end was worth the torture". 🙂
Several hours is the longest tickle torture I have given.
Don't remeber the exact time since my clock wasn't the thing I wanted to consentrate on. Alot of other things happend as well (no not sex), but tickling was the main thing.