How long will it take for changes in robots.txt to affect search results?

As per Google support:

First, the cache of the robots.txt file must be refreshed (we generally cache the contents for up to one day). Even after finding the change, crawling and indexing is a complicated process that can sometimes take quite some time for individual URLs, so it's impossible to give an exact timeline.

https:/support.google.com/webmasters/answer/7424835?hl=en

What can I expect after I place my order for my removal request?

Changes to the robots.txt file is applied immediately for you. This means the instruction for Google to exclude this webpage is set from this end. Your receipt has the reference number plus specified detail for your request to be actioned by Google.