The store opened at 7 a.m. yesterday.
The store was open at 7 a.m. yesterday.
Which one do you native speakers prefer?
the two have different meanings.
"The store opened at 7 a.m. yesterday"
At 7 a.m. the owner/employee opened the store.
"The store was open at 7 a.m. yesterday."
At 7 a.m. the store was open. It could have opened at 6 a.m. though.
Hope that's clear,