Bloomberg Volatility Surface (OVDV function): How is time to maturity measured?



This question is probably more for professionals who have been working with Volatility surface.

Please consider this:

This is an example of vol surface for option on FX forwards by Bloombergs OVDV. My Question: How is time to maturity set in this function?

The implied vol's have been put in the Black-Scholes formula and here it is really important how a year for instance is measured. Is it T-t = 1, T-t = 365, T-t = 252 (trading days) or someting else.

Which exact numeric value does 1day, 1week, 1month, 1year have?