You can prove your date of invention by describing and illustrating your invention in your inventor’s notebook. Then sign and date each page yourself. Once you have done that, you should then have a witness read your description. When they have read your description and understand its contents and meaning, they should sign and date your notebook. This is the accepted method for proving your date of invention.
A good inventor’s notebook will be bound, so that pages cannot be added or removed. The pages should be numbered, as further proof that pages have not been added or removed. Each page should have two signature blocks. One for you, the inventor, and a second one for a witness to sign as read and understood. You could hire professionals from Invent Help to assist you in the process.
As the inventor, and owner of the inventor’s notebook, you should sign and date each page as it is completed. You should record all invention activities, including marketing activities, people that you speak to regarding your invention, and so on.
Periodically, you should have your notebook reviewed, by a non-relative, who will sign as a witness in your notebook.
One last note. Your invention is protected only to the degree in which it is described in your notes. Better consult with InventHelp about it. Each improvement that you make to your invention will have a different date of invention, and must be recorded accordingly. For this reason, you will want to make sure that you consistently use and update your inventor’s notebook.