"Pauses for seconds," as you've used it, sounds extremely unnatural to me as a native speaker, to the point of not being able to understand it right away. I might have used the phrase for "seconds"=second helping at a meal. One tip if you're ever unsure of a phrase, google it in quotes. "Pauses for a few seconds" has almost six times as many results as "Pauses for seconds," so you know it's the correct version.
As for how many seconds, I don't think I've ever heard it but it sounds to me like more seconds than "a few."
However, pausing for a few seconds wouldn't be cause for "speculation." Perhaps (based on the context) what you really mean is "pauses for several seconds," "pauses for more than one second", etc. Also, the second part of your sentence ("two speculations are commonly made") also sounds unnatural to me. "Speculation" is better used as an indefinite, uncountable noun, e.g. "The office was filled with speculation and innuendo, but no one knew what had actually happened." It's hard to rewrite without more context, but I might have written something more like, "viewers might speculate that one of the following is the case".
Source: native GA speaker