I would probably answer the question with "From 7:30 to 8:30 am." However, "between 7:30 and 8:30am" and "during 7:30 to 8:30am" would work and would sound alright. "At" usually refers to a specific time, so if you were to say "at 7:30am" or "starting at 7:30am", then it'd be alright. But, saying "at 7:30 to 8:30am" just doesn't sound right. But, people would still understand it, so that's good. Good luck with improving your English skills! ：）

Traffic jams are most common between 7:30 and 8:30 AM. Traffic jams are most common from 7:30 to 8:30 AM. Traffic is at its worst between 7:30 and 8:30 AM. Traffic is at its worst from 7:30 to 8:30 AM. The morning traffic starts to get bad at 7:30 AM.

I would probably answer the question with "From 7:30 to 8:30 am." However, "between 7:30 and 8:30am" and "during 7:30 and 8:30am" would work and would sound fine. "At" usually refers to a specific time, so if you were to say "at 7:30am" or "starting at 7:30am", then it'd be alright. But, saying "at 7:30 to 8:30am" just doesn't sound right. But, people would still understand it, so that's good. Good luck with improving your English skills! ：）