Website speed is very important because it affects conversions. Website visitors or potential customers will bounce or not return to any website with a low page speed. Thus, leading to a loss in revenue.
One can’t provide a one-size-fits-all answer to your question because a rise in google ranking in the first 30 to 90 days depends on thousands of factors.
Some of the most important factors that affects one's ranking on Google are:
A Secure and Accessible Website
Keyword Competition
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Since I use WordPress to create websites I always UpdraftPlus WordPress plugin to backup my WordPress files to remote storage locations like Google Drive, Dropbox, or Microsoft OneDrive. It is also easy to restore backed-up entities from the UpdraftPlus console with one-click access.