Cheers lynsDan - I'm on first cycle of 100mg of Clomid after my last cycle of 50mg failed to make anything happen.

I actually think I'm going to ignore the instruction to have another BT on Saturday (by my calculation 3-4 DPO). I'll just go and do the next one next Wednesday (7-8 DPO).
If the Dr can't tell me why she wanted the tests done today and Sat, then too bad. I have no relationship with her and no desire to.