Urge to open eyes

When I meditate after about 45 minutes I start to get this strong urge to finish and open my eyes. I use a timer and after a while I start to feel time dragging and wishing the bell would hurry up. I'm struggling to stay mindful when this happens as the feeling is so strong that it overwhelms and I end up finishing the sit. Any advise anyone can offer please? Ive tried not using a timer which helps but that's difficult as I cannot just sit indefinitely most of the time.