You definitely can. You have to be careful, because not all of the transaction-related DMVs will record a start time for the SELECT-only transaction.

If you run the SELECT-only transaction in one query window, and run the following query, you'll see the start time and the duration in seconds. You can tweak the DATEDIFF to get duration as you see fit:

SELECT st.session_id ,

at.transaction_begin_time,

TransactionDurationSeconds=DATEDIFF(second,at.transaction_begin_time,GETDATE())

FROM sys.dm_tran_session_transactions st

INNER JOIN sys.dm_tran_active_transactions at

ON at.transaction_id=st.transaction_id

Cheers!