datetimes should be consistent in type

[dkent600]

Many dates are supplied as Date and many are supplied as Number. This kind of inconsistency can cause all kinds of issues with consuming software (immediate example: daostack/alchemy#1984)

1. They should all be supplied as either Date or number (Date seems more friendly to me, but number is more agnostic.
2. They should all be declared consistently in their governing interfaces.

[orenyodfat]

I am good with both .. though agree it should be consistence .
If @jellegerbrandy has nothing against Date so lets do Date.
Please note that a time period should be Number.

[roienatan]

The consistency is very important. I think better to use Date.