Most AI summarizers are designed to work almost instantly. Summaries should normally be generated in just a few seconds. For example, Quetext can generate summarizes within a few seconds and give you downloadable word documents for the summaries.
There are a few other things that affect how quickly you can receive your summary (e.g., how long and/or complicated the original content was). The technologies that are used in the production/ creation of these summary tools have generally been designed to be highly efficient while still delivering high-quality performance.