I would think the JVC`s remote sends more than 1 code. Another words firstly an initial code for adv of minutes ...then a further 2nd code is sent when it is held down for some time to advance 30mins etc.
So my sugestion would be merely to create 2 buttons the first button for adv of 1 minute / second button to adv 30 minutes etc. (or create a time delayed macro-a bit more tricky)
For reference this is refered to as discrete codes.
Probably the easiest way to capture the codes independantly is with a book! Use the book to block 1st/2nd part of code when capturing on the different buttons of your pronto. Its trial an error , but usually works in the end.
The other way is to find the discrete codes for your JVC remote then convert to NEO format.More tricky but at least now you know what youre searching for.
Good luck ....
please remember to post back here to let the forum know if this solves your problem.So others may use it as reference material.