at one's earliest convenience
• as soon as one can without difficulty.
• "please telephone me at your earliest convenience"
at one's convenience
• at a time or place that suits one.
• "do make an appointment at your convenience"
Similar:
at a convenient time,
at a time that suits you,
when it suits you,
at your leisure,
in your own time,
when you have a minute,
when you can,
in due course,
