Depends on how severe it is. If it's not severe, you can just shave the tip off with sheavers and then go over it with a razor (like... for legs) to get rid of the short hairs. It might make you look like your forehead is bigger, but if you're into make up you can contour. I don't have a widow's peak, but I do clean up my hairline (I have very short hair) in a similar way. As for how long it takes my hair to grow back... it basically starts within a couple days(the baby fine hairs), but it takes about a month for it to completely grow back to match my hair length.
You might be able to youtube different solutions, too. (Also, you probably don't want to hear this, but I think Widow's Peaks look really sharp/classy, so maybe consider keeping? Nothing to be ashamed or embarrased about, but that's your decision.)