I've got one: according to the info. sent with the form for the new card, it's available in England from 9.30am to 11.30pm Monday to Friday, any time Saturday, Sunday and Bank Holidays. Bristol is slightly different - it's from 9.00am to 4.00am Monday-Friday and any time weekends and Bank Holidays provided that your journey starts in specific areas.
It doesn't include rail and express coach services. I believe the over 50s can get reduced travel on National Express coaches, though, so it's only the trains which are out of it.