Update strategy for SQL server into elastic search

Hi everyone.

I'm trying to code along this [guide]( guide https://www.elastic.co/blog/how-to-keep-elasticsearch-synchronized-with-a-relational-database-using-logstash) but doing it in MSSQL

First off there is no UNIX_TIMESTAMP() function in SQL so I initially tried this
DATEDIFF_BIG(SECOND,'1970-01-01', modification_time) AS unix_ts_in_secs

This however doesn't work because a timestamp (synonym to rowversion) is not possible to convert to a time in SQL..

So here I am wondering how I can make a similiar approach in SQL as shown in the guide.

Thanks in advance