I personally use Google calendar for this. It can do this effectively. If you learn how to use effectively:
Prior to june 22 - 2015: you could add the stuff to your calendar and let you send a text-message at some point to remind you. Now the text message feature has been removed.
BUT there was another feature: pop-up feature which basically sends a popup on your browser or a notification on your phone to tell you an event is starting (0 - 50 minutes before the event).
Now you must be wondering why use this and how to use it. It is simple. you can add five minutes reminders after every 25 minutes of your period of work and if you have an android phone, it will automatically have google calendar on it. The other phones have to install probably if they don't come with it by default.
- Google calendar synchronizes with your phone automatically when you are connected to the internet so you wont have to worry about adding stuff from the calendar on the phone. You can add either through the browser or through your phone. You can configure the number of popups, the times of pop ups and notifications. I saw a friend using it a year ago and I started using it, I have been more productive ever since.
I hope you try this, because you can actually add tasks, times, events and much more. Google calendar is probably the best I have used so far.