* Go to Self service portal settings (Admin - > General - > Self service portal settings) - > " Do you wish to enable On Hold scheduler when your requests are put on hold? " select the radio button as 'Yes', and save the setting.
* Go to a request, and when you change the status from 'Open' to a custom status with stop timer or 'On hold' , you will see a pop up as below, where you can schedule the status change from 'On hold' to 'Open'. Select the date when the status had to be changed as 'open' and click on Update.
As for the notification to be sent to the technician, you may create a custom trigger to send the notification. Go to Admin - > Helpdesk - > Custom triggers - > Add new action, as shown below. So, when the request is edited, i.e changed from custom status (with stop timer) to 'Open', a notification would be sent to the assigned technician.