The length of the game depends on your own progress, so it's difficult to put a number on it.never played the Shenmue games however I know there is a huge cult following, how long does each game last roughly, story wise no side objectives? Also how many side objectives are there minus working for money such as lucky hit etc
The length of the original game is kinda artificially extended by having to wait for certain story beats (basically Animal Crossing-ish waiting for the next in-game day), but that's likely to be gone in a remaster.
The sequel is absolutely dependent on your own progress as some of the major quests are pretty flexible and can be shorter/longer depending on performance, story branches, etc.
Side objectives outside earning money (i.e jobs, gambling, street fights for cash)... there's a handful. You can practice your martial arts moves (alone or with a partner in the original, just with a partner in the sequel), collect capsule toys (both games), play games in the arcades (both games), darts rivalries (sequel only, technically gambling as you play for money), slot machines (both games), duck racing (sequel only, also done for money I guess), and maybe a few more I'm forgetting.
Side quests is a different matter. The original Shenmue handles side quests and optional events as an extension of the main story with additional story beats and character development. The sequel has some legit sidequests alongside the optional activities, one of which is pretty obscure to find out yourself but gives you two extra boss battles and unlocks a new minigame.