Bridal showers

I don't think there's really any such thing as too late, although I do think it would be a bit much to expect guests to commit two consecutive weekends to your shower and then your wedding.

You could have a few weeks prior but would invite now. Maybe mid March

If your sister moves quickly, she can have the invites out in the next 2-3 days and plan it for the end of March. But that’s pushing it.

Usually they are done no later than 2 weeks before the wedding . Also, most showers are fairly informal, and small. People can be invited in a phone call to each guest, with a follow up text or email if needed. Usually at least half the people tell you immediately, I can or cannot come. And the others get back to you. So if you know a bunch are declining , sometime because someone your hostesses don't know has a conflicting event, they can change dates. Or invite a few more people.

I think it’s fine to have it whenever earlier so long as it works for your schedule

I have been to one that was the day before the wedding. They didn't this way on purpose because most people had to travel. I think a 2-4 weeks before should be absolutely fine!

We are having my bridal shower this weekend and we get married on March 21st! I think you want at least 3 weeks between shower date and wedding date so that you're not asking people to travel back to back weekends!

Looks like you get married April 11th, so I would recommend having your shower by March 14th!

I don't believe there's a specified date, but as pp said, as long as it's not TOO close to the wedding you should be fine.