Automatically Increase Document Number/Cell Number on open

I would like to be able to click on something which will open a new google sheet based on a template. I would need cell A1 to contain a number which increases by 1 every time the template is opened. Ideally I would like the title to match this new number.

I am working on developing a purchase order form and want to make sure that no matter who opens the template sheet, they will be given their own PO number in order of when they opened it to avoid multiple people using the same number.

I have limited scripting experience so i have been performing a lot of google searches and trying to map out how to ask this properly. I have tried a macro that makes the title the same as cell A1 but no luck. I still have no idea how to automatically generate an incremental number for the title based on the time it was clicked.

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Author: Oliver H