Be careful about using one sitting for just one exam. If you have to, then fine.
However, just think that
a) you may need those extra sittings for any re-takes
b) If at an airline interview you are asked why you had to use one sitting for one exam, or why you required all 6 sittings? Your answer will probably sound something like "because my learning curve isn't steep enough to take in all the information in a short period of time". This won't look good to a company who will be potentially paying for your type rating.
That said, I know a handful of people in that situation who have done ok for themselves. But when the market gets difficult, airlines get picky.
If you're not ready for an exam, delay it until you are.