S.R.Martin

I honestly find the concept of almost 7 times longer years compared to earth interesting and would encourage you to keep it that way. It just highlights the unique aspects of the planet and setting so well. And to your worries: readers will get confused, until it is explained. But that's ok. And as long as you don't mention 5 years and snu snu in the same sentence, and it is after the explanation, you should be fine.