exten => 80,1,GotoIf($[${DB(office_page/inuse)}=0]?2:5)
exten => 80,2,GotoIf($[${STRFTIME(${EPOCH},,%Y%m%d%H%M%S)}-${DB(office_page/page_end_time)}>3]?5:3)
exten => 80,3,Wait(1)
exten => 80,4,Playback(wait-moment)
exten => 80,5,Goto(custom-page,1,1)
exten => 80,6,Wait(1)
exten => 80,7,Playback(please-try-again-later)
exten => 80,8,Hangup()

[custom-page]

exten => 1,1,Verbose(1,Start)
exten => 1,2,Set(DB(office_page/inuse)=1)
exten => 1,3,SIPAddHeader(Call-Info: sip:<192.168.1.8>\;answer-after=0)
exten => 1,4,Page(SIP/105&SIP/122&SIP/123&SIP/124&SIP/125&SIP/126&SIP/129&SIP/130&SIP/132&SIP/133&SIP/134&SIP/135&SIP/136&SIP/137&SIP/138&SIP/140&SIP/141&SIP/142&SIP/145&SIP/146&SIP/147&SIP/148&SIP/150&SIP/151&SIP/152&SIP/153&SIP/154&SIP/155&SIP/156&SIP/157&SIP/158&SIP/159&SIP/160&SIP/161&SIP/162|s)
exten => h,1,Set(DB(office_page/inuse)=0)
exten => h,2,Set(DB(office_page/page_end_time)=${STRFTIME(${EPOCH},,%Y%m%d%H%M%S)})
exten => h,3,Verbose(1,Done)