We have changed the end of day time for our bank with 3 locations. Are there any requirements as to the size and location of the lobby notices that we need to post?

We just changed ours also. I did not find a specific size, merely changed our existing lobby hour signs. We did post in the paper and on our lobby boards about 2 weeks prior about the coming change. We also notified FDIC (our regulator).

Our hours for which we are open for business has not changed. What has changed is the end of the business day. We did post a notice in the lobbies of all 3 branches. What I am wondering is if there are any specifics on size and location of the signage.

No, not unless required by State law. You most likely have a change in your Funds Availability Policy however.