At a SG of 1.050 your looking at 6.7% if you ferment out to 1.000, this will be a very dry tasting Cider so you may wish to sweeten after fermentation.
Depending on your end type of cider would depend on whether to airlock or not, If you want very traditional farmhouse cider 'rough stuff' IMHO then don't airlock and you will get something which is a cross between vinegar and cider.
I recommend you airlock your buckets and seal down. Cider and air do not mix well, the less time they are in contact the better.
Time of fermentation will very depending on the temperature of the cider