This is a time management question. Most auditors will have multiple clients at once. This is especially true if you're working for an audit firm like PwC or Deloitte. You have to be able to show when you're working for one client and not the other for billing as well as for explanations why something has been paused. Clients don't like to hear or know about your other clients, but most are understanding.
Take me, for example. I work full time at a tech company, but when I'm home and have down time, that doesn't affect my current job of assisting with these postings. I also have a blog that I write. It's all about time management.
"I track my hours using an Excel formula to track how much time each client needs before I start, then I allocate my day accordingly. If timetables need adjusting, I notify the clients when it's necessary."
"In college, I had a planner that I used to track the amount of time I spent on each class and the associated homework. I also used that to track my schedule for work and sports activities. It helped me stay organized and I ensured I never missed one assignment or a single day of work."
"I generally use whatever software the company provides for tracking time, but on my phone, I also use Google calendars to track my time as well as a clock App I downloaded that starts timing when I log it and tracks a full forty-eight-hour history."