how to Find/Replace a part of URL in InDesign

Okay, now that I have looked at the OP's demo file I have realised that the problem was that the hyperlinks were all faulty—none had destinations at all, so they couldn't be adjusted. I cleaned up the file and re-wrote the script so that now it generates suitable hyperlinks based on a URL template string, and it grabs details from the page, including day number, month number and hour of day (using find paragraph styles), and creates a hyperlink based on these details. (It gets the month number from the applied master page name.)

Well, for the sake of people learning scripting, here is the final script below. - Mark

/**
 * Create hyperlinks for calendar elements.
 * Will remove existing hyperlinks previously
 * created by this script.
 * Expects the document to have paragraph styles
 * for daily time and daily day number, as well
 * as master spreads named after the months.
 * @7111211 m1b
 * @version 2022-11-28
 * @discussion https://community.adobe.com/t5/indesign-discussions/how-to-find-replace-a-part-of-url-in-indesign/m-p/13374674
 */
var settings = {

    // year
    year: 2023,

    // the URL string
    urlTemplate: 'https://calendar.google.com/calendar/u/0/r/eventedit?action=TEMPLATE&dates=#yyyy#mm#ddT#hh0000/#yyyy#mm#ddT#ii0000',

    // paragraph style names
    dailyTimeStyleName: 'Daily time',
    dailyDayNumberStyleName: 'Daily day number',

};


function main() {

    var doc = app.activeDocument,
        hyperlinks = doc.hyperlinks,
        matchOldHyperlinks = /T\d\d$/;

    // first remove any hyperlinks
    // create previous by this script
    for (var i = hyperlinks.length - 1; i >= 0; i--)
        if (matchOldHyperlinks.test(hyperlinks[i].name))
            hyperlinks[i].remove();

    // reset grep prefs
    app.findGrepPreferences = NothingEnum.NOTHING;
    app.changeGrepPreferences = NothingEnum.NOTHING;

    // find criterion
    app.findGrepPreferences.findWhat = '^\\d{2}$';
    app.findGrepPreferences.appliedParagraphStyle = settings.dailyDayNumberStyleName;

    // find the dayNumbers
    var dayNumbers = doc.findGrep();

    if (dayNumbers.length == 0) {
        alert('Could not find any day numbers in ' + doc.name + '.');
        return;
    }

    // store all the day numbers in array indexed by page's documentOffset
    var days = [],
        masterNames = ['B-JANUARY', 'C-FEBRUARY', 'D-MARCH', 'E-APRIL', 'F-MAY', 'G-JUNE', 'H-JULY', 'I-AUGUST', 'J-SEPTEMBER', 'K-OCTOBER', 'L-NOVEMBER', 'M-DECEMBER'];

    for (var i = 0; i < dayNumbers.length; i++) {

        var page = textPage(dayNumbers[i]);

        days[page.documentOffset] = {
            dayNumber: dayNumbers[i].contents,
            monthNumber: indexOf(page.appliedMaster.name, masterNames) + 1
        }

    }

    // find the daily times
    app.findGrepPreferences.appliedParagraphStyle = settings.dailyTimeStyleName;

    var dailyTimes = doc.findGrep(),
        counter = 0;

    if (dailyTimes.length == 0) {
        alert('Could not any daily times in ' + doc.name + '.');
        return;
    }

    // find placeholders in the url template
    var findYear = /#yyyy/g,
        findMonth = /#mm/g,
        findDay = /#dd/g,
        findHourStart = /#hh/g,
        findHourEnd = /#ii/g;

    for (var i = 0; i < dailyTimes.length; i++) {

        var documentOffset = textPage(dailyTimes[i]).documentOffset,

            // get the url elements
            monthNumber = ('0' + days[documentOffset].monthNumber).slice(-2),
            dayNumber = days[documentOffset].dayNumber,
            hourStart = dailyTimes[i].contents,
            hourEnd = ('0' + (Number(hourStart) + 1)).slice(-2),

            // make the url based on the template
            url = settings.urlTemplate
                .replace(findYear, String(settings.year))
                .replace(findMonth, monthNumber)
                .replace(findDay, dayNumber)
                .replace(findHourStart, hourStart)
                .replace(findHourEnd, hourEnd),

            name = [settings.year, monthNumber, dayNumber].join('-') + 'T' + hourStart;

        // remove hyperlink if already exists
        if (doc.hyperlinks.itemByName(name).isValid)
            doc.hyperlinks.itemByName(name).remove();

        var existingHyperlinkSources = dailyTimes[i].findHyperlinks();
        for (var j = existingHyperlinkSources.length - 1; j >= 0; j--)
            existingHyperlinkSources[j].remove();

        // set up hyperlink
        var hyperlinkSource = doc.hyperlinkTextSources.add(dailyTimes[i]),
            hyperlinkDestination = doc.hyperlinkURLDestinations.add(url, { hidden: false }),
            hyperlink = doc.hyperlinks.add(hyperlinkSource, hyperlinkDestination);

        hyperlink.name = name;
        counter++;

    }

    alert('Added ' + counter + ' hyperlinks.');
    return;


    /**
     * Returns the document offset
     * of the text's page.
     * @9397041 {text} text - an Indesign text object.
     * @Returns {Number}
     */
    function textPage(text) {

        if (text.parentTextFrames[0].parentPage)
            return text.parentTextFrames[0].parentPage;

    };


    /**
     * Returns index of obj in arr.
     * Returns -1 if not found.
     * @9397041 {any} obj
     * @9397041 {Array} arr
     * @Returns {Number}
     */
    function indexOf(obj, arr) {
        for (var i = 0; i < arr.length; i++)
            if (arr[i] == obj)
                return i;
        return -1;
    };

}; // end main

app.doScript(main, ScriptLanguage.JAVASCRIPT, undefined, UndoModes.ENTIRE_SCRIPT, 'Add Calendar Hyperlinks');