You may store the values in the standardized
ISO-8601 [^] format:
[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]Z
.
This format is supported by most date/time from string parsers. The date/time separator 'T' is often replaced by a space character for human readability (this will break the standard but is widely accepted).
The 'Z' (Zulu) character at the end indicates UTC here. As already noted by Richard, storing as UTC is always preferred.