blood tests

Becky • My angel 18-11-17 👼🏻 My little rainbow 17-09-18 👶🏽🌈
So AF arrived this morning which means that i can have my blood tests done. The doctor said I should test days 3-5, and day 21. She said if my cycle isn't 28 days then I might need to work it out.
My cycles are 33 days...so am I right in thinking I can still do day 3-5 as normal, but  "day 21" should be around day 26 for me? Help please! The receptionists at the doctors aren't very helpful!xx