All are correct, yes.
You can also use "at" when referring to place and time.
She will arrive at my house around noon.
She will be here at noon.
He will get to his office at 8:00 a.m.
1. He was driving at 70 km an hour.
2. He was driving at 50 miles an hour.
3. He was driving at low speed.
4. He was driving at full speed.
(Are they all grammatical? Do you have some other expressions about "at _____"?
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