This phrase is a bit vulgar and it's not often used in common conversations. It literally translates to 'when my ass hole stands up today' which could be loosely interpreted as 'whenever I feel like it today' or 'at my own convenience today'.
Examples
- Spanish: '¿Cuándo vas a terminar tu trabajo?' 'A la hora que se me pare el culo hoyo poto.'
- English: 'When are you going to finish your work?' 'Whenever I feel like it today.'