Python-сообщество

 >>> from datetime import datetime as dt
>>> now = dt.now()
>>> tmr = dt(now.year,now.month,now.day,18)
>>> delta = tmr - now
>>> sec = delta.seconds
>>> sec
19341

 import sys
from datetime import datetime
from socket import *
from PyQt5.QtWidgets import QSystemTrayIcon, QMenu, QAction, QApplication, qApp
from PyQt5.QtGui import QIcon, QDesktopServices
from PyQt5.QtCore import Qt, QUrl, QTimer, pyqtSlot
class RightClickMenu(QMenu):
    def __init__(self, parent=None):
        QMenu.__init__(self, "Menu", parent)
        quit_action = QAction("Выход", self)
        quit_action.triggered.connect(qApp.quit)
        self.addAction(quit_action)
class Client(QSystemTrayIcon):
    def __init__(self, parent=None):
        QSystemTrayIcon.__init__(self, parent)
        self.setIcon(QIcon("icon.png"))
        self.right_menu = RightClickMenu()
        self.setContextMenu(self.right_menu)
        self.activated.connect(self.click_trap)
        self.ellapsed_sec = 0
        self.timer = QTimer()
        self.timer.setInterval(180000)
        self.timer.setTimerType(Qt.PreciseTimer)
        self.timer.timeout.connect(self.on_timer)
        self.timestamp_start = datetime.now()
        self.timer.start(180000)
    @pyqtSlot()
    def on_timer(self):
        self.ellapsed_sec += 1
        delta = datetime.now() - self.timestamp_start
        delta = delta.total_seconds()
        if self.ellapsed_sec != delta:
            self.my_func()
    def click_trap(self, value):
        if value == self.Trigger:
            self.showMessage("Оповещение", "Нажали на иконку.", QSystemTrayIcon.Information)
    def my_func(self):
        self.showMessage("Оповещение", "Прошло 3 минуты.", QSystemTrayIcon.Critical)
    def show(self):
        QSystemTrayIcon.show(self)
if __name__ == "__main__":
    app = QApplication(sys.argv)
    tray = Client()
    tray.show()
    sys.exit(app.exec_())