String to Unix timestamp conversion

Hi ,

I am trying to convert "2017-01-03T00:05:00+01:00" into unix timestamp.

I am using below formula, but its giving wrong date . Could someone please help me with this.

t(timestamp(ASDATE(LEFT(SUBSTITUTEALL(#PreProcessing!granPeriod_endTime;"T";" ");19);"YYYY-MM-dd HH:mm:ss")-15*60*1000)-15*60*1000)

this is resulting in wrong timestamp value "1483396500000"

Also I want to add 5 minutes to this time. Please advise.