How to calculate the time difference between two days in seconds

i have a php page .

Here i will get the start time as query string (eg $startTime= '8/27/2010 1:15:17 PM')

Now i need to find out the total seconds between the current time and started time

Ho开发者_开发问答w can i find out this in php

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echotime()-strtotime($startTime);