Am looking for the solution for this issue from long time, failed to figure out what is actually causing this. Am doing a project where some modules depends on various datetime calculations, user enters the date and time in a csv file like this.

am reading that file and format the date and time using momenttz library, below is the code.

 const getTimestamp = (time_array,date_object) => {
    let year = date_object.substr(0,4);
    let month = (parseInt(date_object.substr(4,2)) -1);
    let date = date_object.substr(6,2);

    let hour = parseInt(time_array[0]);
    let minute = parseInt(time_array[1]);
    let second = parseInt(time_array[2]);
    console.log("hr ",hour, " minutes ", minute, " second ", second);

    let momentTime = moment.utc({ years:year, months:month, date:date, hours:hour, minutes:minute, seconds:second});
    console.log("momentTime",momentTime); // this log shows correct date and time as mentioned in csv (Moment<2021-09-21T13:25:00Z>)
     const firestore = admin.firestore;
    return firestore.Timestamp.fromDate(momentTime.valueOf());
}

then passing this to firebase add/update query. this is working fine in local emulator, showing correct date and time. for example if i pass 13:25:00 it storing same in local firestore emulator.

But on firestore console saves wrong time(18:55:00 UTC +5:30) 5hrs 30min more than what i provided.

even i changed the system time zone to Clint's time zone(Tokyo zone) to check if it is due to time zone, but still it is 9.5 hours more than client's time.

Note: i know firestore don't care about the time zone and it stores timestamp in epoch format. How can i resolve this issue?