Hi ajmellu7, and welcome to the Forum. How lovely to have new hens, i hope you enjoy them.
If they're 18 weeks, you wouldn't expect them to lay yet even if the days were longer - daylight is a big factor in getting chickens to lay. In Spring and Summer most pullets come into lay anywhere between 20 and 28 weeks, but as Chris says, yours may not make it until the days lengthen after the winter solstice. but they will be growing on steadily, settling in to their new home, and without the burden of laying eggs and looking after themselves in the cold weather at the same time.
I wonder what you're feeding them on? they will be OK on layers pellets, but as they're not expected to lay just yet, growers pellets would be the best for them for the next month or so. Best not to feed them lots of treats, however tempting - get them to finish up the nourishing stuff they need to grow. Also, it's good you can let them out into the garden as 2 sq. metres of run space is very small for 4 full-sized hens. Maybe in time you can make them an extension of some sort?
Black rocks, Speckledys and Columbian Blacktails are definitely hybrids. The Sussex could be purebred but is probably a Sussex X Rhode Island Red or similar, so also a hybrid if so. She would probably have been more expensive than the others if purebred.
There's a good thread at the top of this section about looking after chickens in winter, which you might find helpful. Good luck - do post some pics if you can, we'd all like to see them.