Can anyone advise on the most suitable adhesive/mortar for laying quarry tiles outside at this time of year (autumn)?

Hi and welcome..

A single flexible adhesive but don't fix in freezing conditions..

should i not use sand and cement mortar

As above, cold temperature don't help adhesive setting.
Use rapid setting flexible adhesive on a dry day and you might do ok, plus paste the substrate and back skim the tiles.
Welcome and good luck.

You can do but depends if you need the depth on your existing floor...

what type of quarries..do they need sealing

sorry not experienced in tiling as my trade is bricklayer.
the quarry tiles are brand new and dont know if they need sealing.so any advice appreciated.l

thanks for the advice

We use dorset red quarry tiles on site for front door steps, we use bal rapidset or rapidset flex adhesive, sink the spacers & seal about half hour after laying, we do it this way so when the adhesive is dry, 2 hours for rapid & 3 for flexi, we can grout it & get it blocked off for 24 hours to dry.
These times are guide lines only, adhesive will take longer to dry in this colder weather.

most adhesives can not be used if the temperature falls below 5 degrees..

what brand of quarrys are you using logger?, personally I'd not risk it at this time of year as the chances are high that the temp will drop below 5 deg C. I've got a balcony to do but gonna put it off till spring now.

watch for using sealers in this weather...iw as advised not to seal outside as the sealer will never dry with all the moisture and may also discolour the quarrys

thanks