Hi Fly babe,
Different countries have different rules regarding time in position (and length of shift). While 20 mins on and 20 mins off would be pretty cushy, it's not the case.
Places like Heathrow Approach at Terminal Control West Drayton allow controllers to be in position maximum of an hour and a half, then a 30 min break (it be the law!). Some units allow 2 hours in position before requiring a break. And depending upon available staff, a controller may very well be in position for that long.
Canada has no formal stipulation regarding time in position, although once again depending on how busy it gets, after 2 hours in position you can be feeling a little crosseyed. But once again, it's a staffing issue. If you have the bods there, you tend to rotate through so everybody gets a turn
