Hello,
This is an interesting project. I'm an avid open source supporter and Openerp user. I have customised many modules for my company but never thought about this.
I would like to know if you already have a biometric device in use in your company, also are there any security systems involved in the loop with the biometric, like door access etc. If this is only attendance calculation then it could be done in less than a month. It also depends on what customization has been done in the HR module, if the key variables have been left unchanged it would be easier.
Please feel free to contact me anytime if you have any clarifications
regards
Aeromaster