As SeanJA points out in a new post to his blog, there's two functions that were included in the PHP 5.3 version of the DateTime object in PHp that weren't in the PHP 5.2 version - specifically the get/setTimestamp ones.

These are some strange methods to be missing as a lot of people in the PHP world seem to work on Timestamps using these concepts, so you would have thought that php would have included these methods initially. Unfortunately they did not, so here is a fix for that.

He provides two pieces of code, one to replace the setTimestamp function and the other for the getTimestamp to add in this handy functionality as you might need it.