I had one reference that showed test enanthate and test cyp both had half-live's of 4.5 days:
Medibolics
But I find more references for your 8-day figure; including the drugs.com profile. So we'll go with yours.
Shall I pull the product literature insert from any of the 4 different brands of test cyp I have on hand (Watson, Pfizer, Paddock, Sandoz) and snap a pic?