It's from about 1957. It's a 'Panorama', one of the 'Horizon Look' series, but with an incorrect crystal - note the ring of bezel peeping out around the crystal. I haven't seen this model in an ad - I gleaned the name from the tag on one that sold with original box and papers last year - so I don't know whether the bracelet really is original. I don't think Elgin originally sold them with those.
The 724 movement is one they made for a year or so. Elgin introduced the new 13/0 models in about 1955 with sub-seconds, then added the sweep second 630 and 716 models in 1956, then added the 23j 724 in 1957. Then the whole group got superceded in 1958 by the 730 and 750 series with the Durabalance.
It's not that rare - I've probably seen at least half a dozen in the last year. They usually fetch in the neighborhood of $80 or less, but a few months back, one finished with a high bid of $10, but failed to meet its reserve price. So, the nearly $300 it fetched surprised me. It certainly wasn't a premium for rarity or authenticity.
I'm not sure I like the bracelet with it, but it's certainly striking.