John
At a relatively active 56 and 60, we walked the Imbros gorge last year. It is relatively easy compared to the Samaria and from memory it was about 2 hours. Be warned, we hired a "taxi" from a taverna at the bottom, to get to Imbros village. The taxi comprised a very beat up pickup with rough iron benches in the rear and a maniac in the driving seat, not to be recommended, but there are others offering the service, and of course local buses. The walk through the gorge is well worth doing, many features are similar to the Samaria, just scaled down a bit, but still very impressive.
Jan and David