We have over 25 projects were we mainly sell man hours. In QBT service item can I use a general item (time) and make charge the rate in the project to reduce general item

Yes, you can use one general service item and change the rate depending on the project.

To keep your list short, you can manually override the rate on each time entry. Whoever logs the time can simply type the correct rate directly into that specific entry. This requires no extra setup, though it does rely on the person entering the time to know the right rate for each project.

Should you have follow-up questions, don't hesitate to get back to this thread.