I work 12+ hour shifts standing and walking as well without breaks (as a pharmacist, we only get "breaks" when/ if it slows down). Before I would do it without sitting (I would even eat, if I got to eat, standing while checking scripts), but now I have a stool with me just in case I need to sit for a minute. Just listen to your body, carefully, and it should be okay. The "exercise" and activity is good for the pregnancy. :-) Just don't push too hard.
It is perfectly safe for pregnancy as long as you are not lifting anything heavy or exerting yourself. (like excessive exercise that causing cramps & bleeding)
And its very good for both you and baby to stay active, it also helps with labor!
Just make sure you are drinking a lot of water to stay hydrated, and listen to your body if you need a break you need a Break.
They say if that's what you were doing before you got pregnant don't stop. Being active is a good thing it helps during the labor process. Just don't push yourself too hard. Your body will let you know if you're doing to much and needs more rest.