I love where this is going.
The hard 4-8 seconds limit is especially interesting. Unfortunately, Nikaidou can't use his ability to return to the very beginning of his golfing career nor can he get back the love of his life... I guess it is done this way because if this ability had no limits the manga wouldn't have any stakes.
Well, if this ability has no downtime then with enough determination he would theoretically be able to chain it and eventually return to any moment in time he desires. It would be nice if, at the end of the manga, Nikaidou realizes what truly mattered in life and chain-warps himself back to his time at the restaurant and lives out his life with Kasumi.
Also very curious what the downside will be, this is hell golf after all. I could see a situation where maybe he needs to make a hole in one of something to progress, and he spends hundreds of hundreds of years replaying just that one drive...
I love this! I can already imagine it: Final hole before getting his license and the only way he passes is by getting an almost impossible hole-in-one. Nikaidou slowly goes insane as he is unable to let go of his dream. With this, the ability wouldn't even need a cost.