How long can you be in front of computer screen without getting stressed or having eye strain?

It depends. If you are briefly checking email messages there is less likelihood of eye strain than if you spend an hour in front of the monitor. But if you have dry eyes or an uncorrected prescription (farsightedness, astigmatism, presbyopia), you may experience strain or fatigue much more quickly.
Varies. When working at near tasks, it is important to rest the eyes for at least 15-30 seconds for every 15 minutes of near work.

Related Questions

Can eye strain from looking a computer screen for too long cause nystagmus?

No. Nystagmus has many etiologies, but not caused by eye strain. It can be induced by various tests like spinning around on a chair and stopping. Read more...
No. Nystagmus is an "internal" condition that is built in to the wiring of your eyes and brain. "external" issues such as fatigue or looking in certain directions can cause nystagmus to appear worse or more evident, but they cannot cause nystagmus to develop. Read more...

Can staring at a computer screen for too long create a lot of stress in your eyes which can lead to pain?

Perhaps. If you require correction (glasses, bifocals, contacts. ...) and are not wearing these while at the computer you may have eye strain or even develop headaches. You should be checked by an eye doctor. Also dry eye could cause these symotoms - they can check for this too. Read more...