How to manipulate form data before sending to server?

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I want to collect 25 schedule times (hour and minutes). User will input 25 times using drop down boxes. That means, 25 hour and 25 minutes drop down boxes, making total 50 drop down boxes. But I don't need to send them as individual variables. One string like- \[code\]08:05;08:37;09:43;09:59:11:12;12:34\[/code\] will do.So, the variable to send will be like- \[code\]time=08:05;08:37;09:43;09:59:11:12;12:34\[/code\]I think it will be easy - user presses submit button, all the variables from 50 drop down boxes will make a string and then send that string. How to do that? any ideas? any suggestion? Any example or tutorial on this is appriciated.