At the latest
No later than. The tour will start at noon at the latest.
At the expense of (someone or something)
To be to the harm of (someone or something). The man was very successful but it was at the expense of his family and health.
At the end of the day
When everything else has been taken into consideration. At the end of the day, it was impossible to get the money to build the house.
At the end of one’s rope
At the limit of one's ability to cope or deal with something. I am at the end of my rope about what to do about my problems at work.
At the eleventh hour
At the last possible moment. The company and the union settled the strike at the eleventh hour.
At the drop of a hat
Immediately and without any pressure. My friend will always help me at the drop of a hat.
At the crack of dawn
When the first light of the day appears, very early in the morning. We left for our holiday at the crack of dawn.
At the bottom of the ladder
At the lowest level of pay and status in a company or organization. I will start at the bottom of the ladder at my new job.
At the bottom of the hour
At the half hour - 10:30, 11:30 etc. (at the bottom of a clock). The weather forecast is on the radio at the bottom of the hour.
At times
Sometimes, occasionally. At times, our teacher is very nice but at other times she is not nice.