Change simple online game to record mouse clicks with high temporal resolution

For my PhD project (social psychology) we need a small modification to a small online game written in Java Script. Find out more about the game and download the sourcecode on [login to view URL] The software uses PHP and Java Script to display a virtual game of catch to the user and logs all throws in a textfile on the server. The timestamp of the throws is currently only displayed in full seconds. This is not accurate enough for my purposes and should be increased to something close to millisecond resolution. (.1 or .01 seconds would already be of use) Objective: change the program so that the timestamp in the logfiles includes the time in millisecond (or 10/100ms). The timestamp should signify the mouseclicks. Rather small timing errors should be avoided but solutions with very unreliable timing may be rejected. The adaptations should work in most browsers and in the 3 as well as the 4 player version of cyberball 4.0