Rushing is terrible because feeling rushed is a kind of anxiety. When we feel anxiety setting in, our minds drift towards thinking about threats and possible things that could go wrong. You do not want those clouds gathering in the mind of the meeting planner.
We all know we are in a negotiation situation to get something done. After all, even if you like negotiation, a walk in the woods would probably be more enjoyable. Still, you get nowhere by rushing.
A state of felt haste is the exact emotion you do not want to create.
Most people dislike making a decision when under pressure, and may feel cornered. They may, of course, still choose to commit to your suggestion in the negotiation. However, a much more likely outcome is that they will decide not to hire you on the on-the-spot calculation that this is the least risky option.
A great way to avoid creating anxiety and haste is by setting a smaller objective than your counterpart expects. They may expect you to want to get a signed contract. Your goal (for this talk) may be just understanding their situation, to create a stronger case for your services.