If you arrive before Thursday then you will start from Reykjavik
If you arrive on Thursday, then you start from Keflavik (airport location).

If you arrive on Thursday morning you have an option to go to Reykjavik and have a walk round and start there
If you arrive Thursday afternoon, then the plan is you start from the airport,BUT this is not final and might change. It is dependant on car hire agent’s help and procedures.

There is not any option for arriving Friday

We do not stay in Reykjavik Thursday night.