Where can I get SQL Server Transaction Begin Time from?

I am working with temporal tables in SQL Server and the generated time is the transaction begin time in UTC datetime2. Is there a function or table in SQL Server to get that same transaction begin time to use elsewhere that does not require me to write to and select from a system versioned table first? I have some non-system versioned tables that are part of the same transaction, and I would prefer if the datetime2 recorded against them matched instead of using SysUTCDateTime and having it vary. I tried to pull it from sys.dm_tran_active_transactions but it is datetime and local server time and appear to be different. * system versioned: 2017-04-11 14:00:59.4690673 * active transactions: 2017-04-11 15:00:59.467