If you go to your Bloomberg installation directory you should find a BBFIELDS.TBL file
ie mine's in C:\Program Files\Bloomberg\Bloomberg_03\API\BBFIELDS.TBL
Open this with exceland it'll look like this . . .
10|Real Time Quotes|0| |0001|Last Price|LAST_PRICE|3998|27|3
10|Real Time Quotes|0| |0002|Bid Price|BID|3998|27|3
10|Real Time Quotes|0| |0003|Ask Price|ASK|3998|27|3
10|Real Time Quotes|0| |0007|Volume|VOLUME|2974|11|2
10|Real Time Quotes|0| |0009|High Price|HIGH|3998|11|3
10|Real Time Quotes|0| |000A|Low Price|LOW|3998|11|3
10|Real Time Quotes|0| |000B|Bid Yield|BID_YIELD|2440|27|2
10|Real Time Quotes|0| |000C|Ask Yield|ASK_YIELD|2440|27|2
10|Real Time Quotes|0| |0010|Open Interest (Realtime)|RT_OPEN_INTEREST|1542|14|2
10|Real Time Quotes|0| |001F|Best Bid|BEST_BID|3998|27|3
10|Real Time Quotes|0| |0020|Best Ask|BEST_ASK|3998|27|3
10|Real Time Quotes|0| |0023|Mid Price|MID|4062|27|3
10|Real Time Quotes|0| |0027|Last Trade|LAST_TRADE|3998|27|3
10|Real Time Quotes|0| |002D|Open Price|OPEN|3998|11|3
Basically this is a list of all available (incluing undocumented 😉 ) bbg commands that you can use via the =BLP() excel function or via the API.
A judicous bit of formatting in excel (Data, Text To Columns, Delimited) will get it in a more readable format.
I'd find something along the lines of a "time of last trade" or maybe this one "RT_EXCH_MARKET_STATUS - The status of the exchange that the requested security is running on." is worth investigating
Hope this helps, it's a hot Friday afternoon and I'm off to an early start leaving do so sorry I can't check it out further.