Translation:The session takes several hours of work.
I was surprised at this meaning of "llevar". It felt like an overly-literal translation.
But I see from this article http://spanish.about.com/od/usingparticularverbs/a/llevar.htm that "llevar [tiempo]" means "lasts".
Llevar is one busy word!
English has the expression "carries on for" to describe something taking place over a span of time.
But yeah, there are a few verbs in Spanish that, at their most literal level, describe spatial relationships (llevar = carry, dejar = drop / let go, quedar = stay put) that are used in a LOT of metaphorical senses that aren't immediately intuitive to those of us who grew up with English.
I thought that "varias" meant "several" or "various", and "muchas" meant "many", so I'm a bit confused that "varias" is translated as "many" here, although it does accept "several".
To me, "several" feels like fewer than "many"; I assume "varias" and "mucho" are the same.
No. They aren't the same. "Varias" and "Muchas " don't have the same meaning. Soy nativo hablante de español.
In this context: (Ninguna de estas palabras especifica cuánto tiempo; sólo da un aproximado de tiempo /hours/).
Muchas: you can use it if you're sure is going to take too much time. EX: Tengo muchas horas, días y años para estar contigo.
Varias (several or various): You can use it when you aren't sure how much time is going to take. EX: Su avión llegará dentro de varias horas.
I hope to helps. :D