Irule log session time

update, i create this irule:

when ACCESS_SESSION_CLOSED {
 
    set sessionId [ACCESS::session data get session.user.sessionid]
    set startSession [ACCESS::session data get session.user.starttime]
    set endSession [clock seconds]
    set seconds = int($endSession - $startSession)
    set minutes = expr [$seconds / 60]
    set hours = expr [$minutes / 60]
    
    if { $minutes > 60 } {log local0. "the session duration is $hours hours" }
    
    else { log local0. "the session duration is $minutes minutes"}
 
}

but i receive this error:

01070151:3: Rule [/Common/session_log] error: /Common/session_log:6: error: [wrong # args][set seconds = int($endSession - $startSession)]
/Common/session_log:7: error: [wrong # args][set minutes = expr [$seconds / 60]]
/Common/session_log:8: error: [wrong # args][set hours = expr [$minutes / 60]]

what can be the cause?

Thanks you