When to buy a share that is splitting (etc 1 split to 4)? For the recent Apple case, where the stock is splitting 1 for 4, should investor buy-in Apple stocks before or after the split and why?

When to buy a share that is splitting? The short answer is, ASAP. If you are interesting in a stock just because it is splitting, Then you might be in it for the short term. Usually the price goes up.

However, if you are interested in the stock because you like and think the company will grow and do well in 5 years time, then after doing your own dilligent research, buy it regards of the "news" or "hype".​​​

Depends on what is your budget and whether the platform you use allows for fractional share investing.

I bought Apple share after the previous split as the platform at that time did not allow me to do fractional shares. So after the split, the price per share was more palatable to me.

Also take note even after the split, the stock price is also subject to market sentiment and movement. So the price may go any direction after the split.