Senior developer for maintenance and development of and online education platform

Our organization own an online education platform written in php. The structure is complicated and has many modules, api communications, online payment gateway etc. We aim to provide innovative teaching tools and some of these must be completed immediately. We need an experienced in php / codeigniter developer (expert) with many years experience as the basic developer to work on fixes and new modules by deadlines. We need 24 hours / week (4 hours / 6 days).