I'd like to add to this. I feel the distinction between a sub and a slave does not apply to how often you do things. The distinction between both is important indeed: A sub is one who is still considered when he obeys, one whose feelings and sometimes decisions still apply to an extent (that can vary between little and a lot). A slave is one who can't complain, can't refuse, and has to fully obey no matter their feelings and emotions and are indeed only allowed to feel.
But, it's easy to imagine a full time sub. It's just one who lives the lifestyle 24/7, but whose feelings and opinion and emotions matter. And likewise, you can also have someone who just lives their life and becomes a full slave only during sessions.
I often considered that difference in how often you do things like this: You can have sessions, and not be a sub or a slave outside of them. You can have a "play partner" (or recurring dom or sub), which is halfway between sessions and a long term thing, and consists of living it sparingly as the situation comes. And then there's full long term, 24/7 style, where you just don't stop being a sub or a slave no matter what. But for all of the above, you can either be one, or the other.