I would say that 100% would be getting all upgrades, stunts, and collectibles and side missions. Like, a non-cancer way of going about it could be

Run 1: Good karma upgrades, good side missions, all dead drops and shards. Run 2: Evil karma upgrades, evil side missions.

End timer after final piece (last evil side mission, for example) is done.

You experience / collect everything for the sake of the speedrun, even if the counter doesn't get to 100%. I mean its still an awful amount of stuff, but I think its a bit more reasonable.