You can test when your period is due or late for an accurate result. A 35-day cycle simply means you ovulate later than a woman with a 28-day cycle. But everyone ovulates about 14 days BEFORE their period, give or take a few days, so every woman should test for pregnancy when her period is due or late.
Do you track when you ovulate, if you do, then you can do a HPT at 12 DPO. If you are unsure of when you ovulated, then you should wait till you are late for you next period. If you do the test at 12 DPO, it may not be as accurate as if you wait for you next period date. Good luck.