Temporal Representation in existing Granule Files?

@captainkirk99 Question:

STARE time is based on TAI. What is the representation of time in the granules we construct sidecars for? What data type? Float? Integer? Also, what is the epoch? I.e. what is "zero?"

We might need to provide a new method in STARE's temporal API to ease indexing the Granule timestamp.