A recent study at Duke University looked at how people view their goals - and how that affects their concept of time. People who thought about conflicting goals - "what else could I be doing right now?" - had more anxiety and the feeling of having "less time" than those that didn't think about conflicting goals. Multitasking (clicking through webpages while on the phone) exacerbates the feeling of goal conflict and the sense of time pressure. The solution: focus on just one thing at a time, and let go of worrying about what else you could be doing.
Additional research has shown that a person's perception of time is influenced by his/her emotional state, and specifically, feeling stress or anxiety produces the feeling of having less time, and vice versa: feeling like you are behind schedule produces more stress.
If you start to feel stressed about how much time you have: take a few deep breaths every hour and pause (to reduce the surge of hormones that induce anxiety), give full attention to only what is in front of you, and stop thinking about what else is on your To-do list. Your stress level will drop and your perceptions of time will improve.