Bugfixing and modifications for OS-Commerce shops

Hi, We have a lot of OS-Commerce shops running. We have a lot of little modifications to do, bugfixing, ... on a daily base. I'm looking for a programmer who is available each day (no weekends) and who can easily be reached. During working days, office hours, I expect a answering time of 4 hours max. Questions are almostalways for modified OS-Commerce shops. We also have some Phplist users. I like to open a project for 20 hours. I will release a milestone every 3 hours worked. I want that the time tracker of Freelancer is used. According to this, the hours are counted. As soon as the 20 hours are worked, I will start another project. If I'm satisfied, I will award each time the same freelancer. I expect the work will be about two hours a day.