There is no minimum
The most important thing to remember is that as a freelancer you set your own availability.
There are a couple of different types of tasks.
There are tasks that come through from paid clients and there are the tasks from trial clients that come through from potential clients trialling the service. These come through at all times of the day, which means you will get emails in the morning, afternoon and night. However, you have the option to either accept a task or decline it.
You don't need to feel pressured to constantly pick up tasks. As a freelance Virtual Assistant you may pick up and accept tasks when you are available to do so, when you have time to complete them and the experience to do them.
REMEMBER, if you do accept a task from a trial client, you are trying to win over that potential client and gain their ongoing work and income for yourself, so we recommend responding to them quickly and completing the work within a short timeframe.