Yes, that's ok. Sometimes people will take the Five Reflections and expand them in equal amounts of time. So it's ok. It might be very helpful though to make a resolution to yourself that you're going to do more than one in one sitting so that you're not just doing another one because you're bored with the one you're doing, or you run out of things to do or you're having difficulties with it. If you're finding you're having difficulties thinking about a particular way to contemplate a particular reflection you can always ask yourself a question. Often by asking questions about the particular reflection, it can ignite more contemplation. There was a Monk who apparently became enlightened through contemplating a particular aspect of the Dhamma for four days and four nights continuously. Getting deeper and deeper into understanding this particular thing.
It's also ok to try to expand our capacity to reflect more deeply about one particular object. However as we increase our abilities to do this it's fine to do more than one in one session. I'm not saying you have to do it in four days and four nights. This person had been practicing for about 20 years and was a Monk.