"It took me all of ten minutes to find out" - what does "all of" mean?

The sentence: "It took me all of ten minutes to find out"

What does "all of" mean here exactly?

Is it mainly used in a sarcastic context?

Here, "all of" means "as few as", "merely" or "just". It doesn't have to be used sarcastically in general, and more context is needed to be able to say whether it's being used sarcastically in this particular case.

Here are a few examples of the idiom being used in non-sarcastic context, found by quick googling:

• What's incredibly sad is how quickly I was able to concoct that message — it took me all of two or three minutes.
• Except for steaming the green beans, it took me all of about 2 minutes to put together.
• It took me all of two seconds after I first arrived at the [product name] website to say, “I've gotta have it”.