Add milliseconds to DateTime within Explore Custom Dimension

[chriswragge]

I’m trying to do something like this within an Explore Custom Dimension:

add_milliseconds(
  ${Hits.HitTime}
    ,${SessionDetails.VisitStartTimeUTC_time})

but of course, add_milliseconds is not a function. 

When I try and and use the functions available like so,

add_seconds(
  round(${Hits.HitTime}/1000,0)
    ,${SessionDetails.VisitStartTimeUTC_time})

I get the following error

Query execution failed: - Interval value must be coercible to INT64 type

Is there a workaround for this that does not involve a Table Calculation?