Waiting for properties to sit vs offering under ask quickly

Is it better to wait for an overpriced house to sit before offering a lower price or is it better to make a quick offer even if it is 20% under ask? I am looking at a duplex priced at $130k. I got a first look right before it hit the MLS. I believe fair market value is closer to $100k. Should I make the offer before anyone else can see it or wait until it sits so the sellers can potentially get some feedback that it is overpriced?