Thank you for the information and your question. There is no 6th Amendment right to an attorney or to remain silent until a suspect has been arrested. Merely being a suspect is not enough in the civilian setting (different rules for military cases.) So, until the arrest was made, you would not have had a right to be advised of your Miranda Rights, which do include both the right to an attorney and the right to remain silent.
All that said, unless you are going to be questioned after you are arrested, there is no requirements that your right to remain silent be given to you via Miranda Rights. It is a standard procedure, but there is no law that says that absent questioning Miranda warnings must be given. The only consequence of not giving Miranda Rights and/or right to remain silent and to ask for an attorney, is that any incriminating statement made by the arrestee cannot be used against them at trial
As for the correction of the date and time, they just likely reviewed the evidence and saw that the amended time more correctly reflects when you were discovered in your vehicle, which is the correct time to use and not the time you were arrested. That is necessary, as that is the time that is used for purposes of the speedy trial
rules and also the statute of limitations. So, it works better for you since it pushes the time back and theoretically puts more pressure on the State to file charges and get you tried.
Please let me know if you need any clarification. I would be glad to assist you further if I can.