At any time.
"Whenever you are ready to leave, just grab your coat and we can head out immediately."
In plain English: Whenever means at any time that something happens or you choose to do it.
"Call me whenever you need help."
At any time that.
"Whenever you have a spare moment, please check if the report is ready for review."
The word whenever comes from Middle English and is formed by combining "when" with "ever." It originally meant at any time that a specific condition was met.