Well, yes, if you wear safety glasses too long time, it will just be harmful for your eyes. So just be careful about it and pay more attention to it. Of course, by wearing glasses, it will just protect your eyes from some damage light when you are working. But on the other hand, if you wear them too long, and it has gone over the limited time, it can be bad. In common, they are designed for some functions which are used in a certain time. And it depends on what types you have chosen. So you should just follow the instruction of the glasses.
Yes, wearing safety glasses for long time is not good for your eyes although the safety glasses will protect our eyes from the radiation from the computers. Usually you should take off the safety glasses and then have the good rest after wearing for about one hour. Or else, your eyes may get tired which will be bad for your eyes vision.