Hi,

Please refer to the code:

from odoo import models, fields

from datetime import datetime

class AccountAnalyticLine(models.Model):

    _inherit = 'account.analytic.line'

    start_time = fields.Datetime("Start Time")

    end_time = fields.Datetime("End Time")

    def action_timer_start(self):

        res = super().action_timer_start()

        for line in self:

            # Only set start_time if it’s not already set

            if not line.start_time:

                line.start_time = fields.Datetime.now()

        return res

    def action_timer_stop(self):

        res = super().action_timer_stop()

        for line in self:

            line.end_time = fields.Datetime.now()

        return res

Hope it helps.