Consider changing date to time in standardized output object

[kaitejohnson]

Since the date column in the standard column is not a date but is a 0-indexed vector of days.

Do think there is an argument that passing back dates is more clear with respect to indexing, but since not all R(t) package objects return the date/the data, this probably isn't possible in how we have set things up (which doesn't require the input data, just the model object).