... well time is one thing but if you never even touch the left-hand-side shifter, you won't get the practice and experience... Go alone, find somewhere flat where there are no cars, and fool around with them. Then find somewhere with a (very) small hill and keep playing. Just remember that you should always be spinning at about the same speed on the pedals! Obviously, you can't do this with just 2 gears (unless the hill is veerrrrryyy small!).

No lethal explosion can happen from mismanaging your speeds...

It's really worth learning, you'll probably get less tired legs on longer rides and a better cardio in the end, allowing you to spend more time on the bike. Yeah!!