Please see the temporary solution at the end.
Summary (added 12/24/22 for clarification):
USPS's tracking API is not returning responses in the same format as their documentation. The actual format makes it difficult to extract the event date since there is no EventDate XML element. Worst case, I can use regex, but was wondering if there was a way to receive API responses as showing in USPS's documentation.
Details
In USPS's 
Matched item with groups - it use in code.
Time parsing
(\d{2}|\d{1})\:(\d{2})\s*(am|pm)
Matched item with groups - it use in code.
References
Find string between two substrings