GTD draws a hard line between calendar items and todo items, saying to keep calendar items few and sharp and don’t miss them, and leave lots and lots of unscheduled time to work off your lists.
… are things that has to be on a specific time, usually something that someone else relies on, like an appointment, or like in our building where we need to schedule laundry machines.
… are things that you want to do as soon as possible. GTD likes to sort them into contexts so you can get all your grocery stuff done at the grocery store, for example. But remember here that there are also checklists, where you can put things like a daily or weekly routine. Don’t knock checklists, dumb as they seem. If it’s good enough for airplane pilots it’s good enough for you. For some projects, you might even have a project list with more steps than just the very next step.
Now, there’s nothing wrong with actually scheduling some time to work on your lists, or even to work on specific things from your lists; GTD just asks you to make that a separate thing from your other calendar items. One of the benefits of GTD is how it’s more fluid and flexible and post-modern and if every single thing I’d have to do in a day was as rigid and immovable and urgent as a dentist appointment, I would die.
That said, early on I really was helped by having set alarms that would remind me to “work on my lists”. I didn’t even box in specific projects, just “work on list stuff”, and that made all the difference in the world. GTD has five steps and fifth step is actually doing the things, there’s just no getting around that, and if you don’t remember to actually do the things the whole system is gonna be useless and that’s where an “hey, do list stuff” li’l reminder can help especially early on. Or specific list stuff if you so prefer.