Lost mother cat

Question
Just adopted a ferel cat with 4 x kittens 10 days old.  Whilst putting them into
their new home (a stable) the mother escaped and ran away - have left food out
and a window open but its not so warm - how long will the kittens be OK for
before I should hand feed

Answer
You should start immediately if the mother cat has not returned. Babies of that age will die quickly without warmth and food at least 5 times a day.  They are as fragile as babies of a similar age.  Get some New Born Kitten milk replacer or use goat's milk.
They will do well, if you keep them warm and feed consistently. Remember to wash them around the genitals after each feeding to cause them to eliminate. that is also mama's job and is now yours.

Best of luck,
Barb