In theory you should not need to convert date/time values, but in practice...
HL7 does actually clearly state that dates and times should by formatted in this format:
So if all implementations followed the standard, integration engineers shouldn’t have to deal with converting incompatible date time formats.
But in practice real implementations of HL7 do break the standard like this lab message. Also there are older pre-HL7 formats that are even worse in terms of containing a mix of formats in the same message.
So it this is a problem that has to dealt with. Fortunately an elegant solution exists.