Where is says this at the end of the Add Child button
& "&z=" & Rurl()
Just comment that out or erase that part of the code.
URLRoot() & "db/" & [_DBID_TIME_RECORDS] & "?a=API_GenAddRecordForm&_fid_11=" & URLEncode ([Record ID#])
& "&_fid_21=" & [Related Client]
//& "&z=" & Rurl()