No, if you booked from CruiseAmerica or from your local RV rental dealer then they will almost always refuse any early booking or offer it at a hefty charge ($100!).
On the other hand if you booked from Outdoorsy or RVShare then you are dealing with regular folks like yourself who may be more open for an early pickup. If you are looking to pick up an hour or two earlier then you may be able to gently negotiate with the RV Owner. However if you need to pick up at morning 7 AM then you should offer a reasonable fees to the RV owner to make it a win-win situation for both of you.
Note – Ideally you should negotiate this before you book the RV so that the contract document states the exact pick up time, however if you have already booked the RV then you can still carefully negotiate with the owner and have the communication in RVShare or Outdoorsy website so that there is a trail of this agreement.