Thanks everyone.
I find no direct solution to my problem but based on one of Jeds scripts and google I got something working. The complete tiddler is here but the main part is here below:
I don’t know js so maybe someone can tell me if anything is bad about it. The idea is to call the function with a number and get the current time (hours:minutes) with that many added minutes.
One detail that I don’t know how to achieve is a padding 0 for single-digit hours, but I can live without it.
(function(){
"use strict";
exports.name = "add-minutes";
exports.params = [
{name: "minutes"}
];
exports.run = function(minutes) {
var currentDate = new Date();
var output_hours = new Date(currentDate.getTime() + minutes*60000).getHours();
var output_minutes = new Date(currentDate.getTime() + minutes*60000).getMinutes();
var result = output_hours + ":" +output_minutes;
return result;
};