Is it bad for a guy to have an erection for an hour or two? What does an erection feel like for them?
Depending on the circumstances having an erection for several hours might be embarrassing or it might be nice but except for a few uncommon medical conditions it's not bad.
What *might* be bad is a condition where the area around the base of the penis and testicles begin to ache after really prolonged stimulation. That's sometimes called "blue balls" but since women can get it to that's not the best name for it. (The medical term is vasocongestion.) Now, sometimes guys will claim they need you to provide "relief" but as Heather puts it in her book no matter your gender, your vasocongestion is not your partner's responsibility. No one else can "give" you blue balls and nobody should be manipulated or pushed into doing something to relieve it.
Finally, about how it feels to have an erection?
That's kind of tough -- sort of like trying to explain what the color red is to another person. From comparing notes with women friends I get the impression it's surprisingly similar to what you probably feel when you're aroused. Just like women or like anyone, men vary in how they like to be touched, in ways that make sense considering our different shapes, but that's different from what it feels like to just have an erection.