X Y Problem

First, prefacing this with a small explanation of the X/Y problem. I have reason to believe that you have a solution in mind for your problem, and you want us to help you realise your solution rather than solve your problem. That's great, in fact that's almost the only reason I'm answering this question because at least you engaged your brain.

That said...

String Patterns

If you know how a string should look, a great way to capture parts of a string is by using Lua string patterns. These describe a format of a string, and parts that you want to get out of it, and allows Lua to do the heavy lifting for you. As an example, the simplest pattern you probably want is (.*);(.*).

day, time = yourString:match("(.*);(.*)")

Substrings

This said, if you know the position of the delimiter you can just get a substring with string.sub. To get that, you want something like

day = yourString:sub(1, delimiter-1)
time = yourString:sub(delimiter+1, -1)

The X/Y problem (again)

Why is your input formatted that way? Why is it a string? Is it possible that you could get it formatted in JSON, or stored as a table rather than a string? This would save you a lot of trouble.

For reference:

• JSONEncode to turn a table into a string
• JSONDecode to get a table from a JSON-encoded string.