「のそ」 is an onomatopoeic word describing a slow and/or sluggish kind of walk or body movement.
We also use 「のそのそ」 and 「のそりのそり」 as its variants.
You can forget "a moment later" for good as it has no such meaning.
For the onomatopoeia-curious out there, 「きびきび」, which means "chop-chop", "speedily", etc. would be like the 'antonym' of 「のそのそ」.