I work off my action lists during non-discretionary time. Depending on how schedule-driven your life is you might need to block off some time so that you can work on them (either specifically or in general) but it's not required. If calling clients is a mission-critical activity (for sales it likely is) and you *truly* can't do it in the morning then you may have to block off time for that activity in the afternoon and focus on less important things in the morning.
Not every action needs to be nor should it be scheduled. Your calendar is for three things: time-specific actions (appointments, meetings), day-specific actions (this must be done on this day or it dies) and day-specific reminders (birthdays, anniversaries, a colleague's vacation days, etc).
I sometimes have next actions that sit on my lists for weeks because I know I'm going to need a large block of time and energy (and perhaps weather conditions) to handle them and the opportunity just hasn't presented itself.
Bear in mind that GTD doesn't run your life for you. It gives you the means to make a good intuitive judgment call about what you should be doing in any given moment. It gives you permission to feel good about going to that meeting instead of doing defined work when you intuitively feel that there's more value added in the meeting than the actions. It also gives you permission to feel good about saying "no" to that meeting when you intuitively feel that it's not the best use of your time. You can only feel good about what you're not doing when you know what you're not doing.
If you don't have an inventory of your actions you might attend that meeting just to avoid having to think about what's lurking in your psyche. You won't, however, be able to avoid that GSA (gnawing sense of anxiety) factor while you're in that meeting instead of making those sales calls on your list.
Best of luck in your GTD journey.