thanks to EE, I googled "execute sql task datetime parameter" to find out how to configure the Execute SQL Task to apply the result of the query to the variable, so I could pass it as a parameter downstream.
Used this url
https://www.simple-talk.com/sql/ssis/ssis-basics-using-the-execute-sql-task-to-generate-result-sets/.
General
ResultSet Single row
Connection Type: OLE DB
Connection: (my named oledb conection)
SQLSourceType: Direct Input
SQL statement : SQL Query
Parameter Mapping
variablename: user:: DateStamp
Direction: Input
data Type: VARCHAR
Parameter name : 0
Parameter size : -1
Result Set
Result Name SQLDateTime
VariableName User::DateStamp
Expressions
N/A