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Hopefully, I will be back in office by 10 am. is the most popular phrase on the web.

Hopefully, I will be back at office by 10 am. 1959,000,000 results on the web	Hopefully, I will be back in office by 10 am. 1960,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
No matter how clever a man may be, far from his neighbors he will never manage to conserve his heat and his flame. I will be back at church next Sunday. All right. I will be back at 3:00. I will be back at that base with warrants! I will be back at 3 and I expect there to be no trace of you left here. If anyone should phone, say I will be back at one o'clock. I will be back at my hotel 'cause I've got an early flight to catch. After that, I will be back to work. Not long, I will be back soon.	For the next question I will be back in a couple of minutes. Because as you stated earlier, I will be back in my desk on Monday morning, playing video games and no one will be any be the wiser. Dan and I will be back in a London minute. I will be back in just a few minutes. I will be back in time for your big moment, I promise. Okay, I will be back in 20. Well, I will be back in the morning to report for duty. So I will be back in a minute.

Hopefully, I will be back at office by 10 am.

1959,000,000 results on the web

Hopefully, I will be back in office by 10 am.

1960,000,000 results on the web

More popular!

No matter how clever a man may be, far from his neighbors he will never manage to conserve his heat and his flame. I will be back at church next Sunday.
All right. I will be back at 3:00.
I will be back at that base with warrants!
I will be back at 3 and I expect there to be no trace of you left here.
If anyone should phone, say I will be back at one o'clock.
I will be back at my hotel 'cause I've got an early flight to catch.
After that, I will be back to work.
Not long, I will be back soon.

For the next question I will be back in a couple of minutes.
Because as you stated earlier, I will be back in my desk on Monday morning, playing video games and no one will be any be the wiser.
Dan and I will be back in a London minute.
I will be back in just a few minutes.
I will be back in time for your big moment, I promise.
Okay, I will be back in 20.
Well, I will be back in the morning to report for duty.
So I will be back in a minute.