25 loud explosions in as many minutes
It means 25 loud explosions were heard in 25 minutes, around noon. The in as many minutes phrase is used to depict the exact numerical amount of time(in minutes) through which explosions were heard.
Take a look at the title of this article:
NASA launching five rockets in as many minutes in ATREX weather study
From the first paragraph of the article:
The $4 million ATREX — Anomalous Transport Rocket Experiment — program
will launch five different rockets within a span of five minutes from
the Wallops Flight Facility in Virginia; the rockets will then release
chemical tracers between 50 to 90 miles up into the sky.
As you can see from the quoted sentences, "launching five rockets in as many minutes" is a concise way of saying Nasa will launch five different rockets within five minutes.
Therefore, the phrase "in as many minutes" is especially used in sentence construction when you have the same number repeating in another part of the sentence, describing a different construct(ex: time/number). Although the other way of writing the sentence(the number expanded both times) wouldn't be deemed incorrect, this way is preferred for its brevity.