How to set the timezone on the Pico

Maybe this could help others searching for DST stuff (for Europe at least):

var offsetUTC = 1; // the offset to UTC in Standard Time (winter)
var useDST = true; // if true, DST will be taken into account when setting TZ

// these formulae are valid until 2099 (or 2022  https://en.wikipedia.org/wiki/Summer_time_in_Europe
function dayEndWinter(year) { // last Sunday of March
        return Math.ceil(31 - ((((5 * year) / 4) + 4) % 7));
}

function dayEndSummer(year) { // last Sunday of October
        return Math.ceil(31 - ((((5 * year) / 4) + 1) % 7));
}

function checkDST(date) {

        let year = date.getFullYear();
        let dateStart = new Date(`${year}-03-${dayEndWinter(year)}T01:00:00 GMT`);
        let dateEnd = new Date(`${year}-10-${dayEndSummer(year)}T01:00:00 GMT`);
  
        return (date >= dateStart && date < dateEnd);
  
}

function setTimeZone(offsetUTC, useDST) {
        E.setTimeZone(0); // start with UTC
        if (useDST && checkDST(new Date())) {
            offsetUTC += 1; // we're in DST
        }
        E.setTimeZone(offsetUTC);
        console.log('Time after setting TZ: ' + (new Date()).toString());
}

// sets the TZ with respect to DST
setTimeZone(offsetUTC, useDST);

// get some start and end dates
for (let y=2018;y<2023;y++) {
        let dateStart = new Date(`${y}-03-${dayEndWinter(y)}T01:00:00 GMT`);
        let dateEnd = new Date(`${y}-10-${dayEndSummer(y)}T01:00:00 GMT`);
        console.log(dateStart.toUTCString() + ' till ' + dateEnd.toUTCString());
}

// test some dates
let dateStrings = [
        '2019-01-01T00:01:00 GMT', // DST false
        '2019-03-31T00:01:00 GMT', // DST false
        '2019-03-31T02:01:00 GMT', // DST true
        '2019-08-01T00:01:00 GMT', // DST true
        '2019-10-27T00:01:00 GMT', // DST true
        '2019-10-27T01:01:00 GMT', // DST false
        '2019-12-01T00:01:00 GMT', // DST false
];
dateStrings.forEach(function (dateString) {
        let date = new Date(dateString);
        console.log('Checking date ' + date.toString() + ': ' + checkDST(date));
})