To avoid any confusion around parsing of dates/times, LUSID expects all timestamps to be in the standard format documented by the W3C here. This format includes the date followed by a time with precision down to 6 decimal places in the seconds field.
Dates are primarily used in LUSID in the AsAt and EffectiveAt/EffectiveFrom fields (cut labels can also be used when specifying an EffectiveAt date).
Examples of valid formats are
YYYY-MM-DD, eg 2021-03-01
YYYY-MM-DDThh:mmZ, eg 2021-03-01T10:01Z
YYYY-MM-DDThh:mm:ssZ, eg 2021-03-01T10:01:30Z
YYYY-MM-DDThh:mm:ss.sZ, eg 2021-03-01T10:01:30.1234567Z
LUSID stores all dates/times in ISO UTC format.