Am I wrong for being irritated that two customers kept asking me when their vehicle would be done?

I told them it would be about 2½ hours (we were packed). They said okay.

Within the last hour, they asked me, twice, when it would be done. My estimate was the same every time and the car was done exactly when I said it would be. Nothing changed.

99% of the time, I give the benefit of the doubt and always find a reason to be happy to help. But this just irked me.