Hey Fiona, you got a lot of mishmash and some great insight above, hope you can sift that!
To answer your question: There is very little difference in setup time betweeen Arcs and LEIs. In comparison to flying time, unless you fly for 1 minute and go home, the difference in setup time is negligible.
As you know, Arcs need to inflate well by wind pressure alone to launch, while LEIs need YOU! Only in a good steady, maybe stiff breeze will the arc win (with experienced pilot!). Some arcs need more inflation to launch ok. If your LEI is BIG, or doesn't have 'one-pump' then it may take longer.
As above, there are OTHER variables if you want to try Arcs!
Oh, they take longer to pack up! Quite a bit longer really :-)
Andy.