Hi,
One way to achieve what you're after may be to first capture the value of the date from one of the tables in a separate variable:
dt=data table ("Name of First Table");
date=Format(Column(dt,"Name of Date Column")[1],"dd.mm.yyy");
After the join, you can rename the table using the "set name" argument:
joined_table=dt<<join(...);
joined_table<<set name(date || " Date 1 and 2");
Please try that and let us know if it works for you.