inopportune moment

Then I say, 'I regret to have arrived at such an inopportune moment.'

At no time would this request have been granted but it came at the most inopportune moment imaginable.

"A gen'man to see you, sah," announced Aunt Fanny at this inopportune moment, and the entomologist was obliged to leave the room.

Bob moved from the window, the ring still in his fingers, and at this inopportune moment, the monocle-man walked in.

She never would have asked him that if she had not known she could bear inspection at such an inopportune moment.