At the appointed time
At the time that has been decided. We went to meet our lawyer at the appointed time.
At the appointed hour
At the time that has been decided. At the appointed hour, the team arrived at the stadium.
At stake
To be able to be won or lost, to be at risk. Much money was at stake during the negotiations for the new stadium.
At (someone’s) earliest convenience
When something is convenient for someone. I plan to speak to the bank manager at his earliest convenience.
At (someone’s) beck and call
To be always ready to serve someone or do something for someone. The woman is always at her husband's beck and call.
At sixes and sevens
To be lost and bewildered. We were at sixes and sevens when the local grocery store closed.
At sea (about something)
To be confused about something, to be lost. Most members of the class were at sea when the teacher tried to explain the difficult theory.
At (someone’s) service
Ready to help someone in any way possible. A member of the hotel staff was at our service during our visit.
At sea
To be on the sea, to be away on a voyage on the ocean. My grandfather was at sea for several months when he was a young man.
At risk
In danger. The children were at risk of getting sick when the disease spread in the school.