Use calendar efficiently, understand project timeline and business priority to determine timeline for my deliverable. In my experience even though I support multiple projects, the projects are at different stages and thus I can stack the time and make sure that I am able to support each project. If there is an overlap with a deliverable, then I keep my management as well as project managers in the loop and let them know if I see an obstacle which might interfere with getting the job done on time. In my experience, communicating on time and appropriately is the key in these types of situations.