Try this
var text URL =
If([Status]="Ready to Start",
URLRoot() & "db/" & Dbid () & "?act=API_EditRecord&rid=" & [Record ID#]
& "&apptoken=b2ef6ijciijsibdf9dftgdjtdhm3"
& "&_fid_15="&URLEncode("In Progress")
& "&_fid_284="&URLEncode(Today()),
[Status]="In Progress",
URLRoot() & "db/" & Dbid () & "?act=API_EditRecord&rid=" & [Record ID#]
& "&apptoken=b2ef6ijciijsibdf9dftgdjtdhm3"
& "&_fid_15="&URLEncode("Completed")
& "&_fid_285="&URLEncode(Today())
& "&_fid_29="&URLEncode(Today()));
"javascript:" &
"$.get('" &
$URL &
"',function(){" &
"location.reload(true);" &
"});"
& "void(0);"
please check the code for the In progress - are you wanting to update two different date fields?
