If you have always worked this type of shift then it will not be a break in routine for your son as this will be all he has ever known,in effect it is a routine to him.
Before you go off thinking that I know nothing about autism let me assure you that I do as I am the mother of a 12 year old son who has Aspergers Syndrome(high functioning autism).
Any carers/child-minders you now employ for your son must be informed of his diagnosis and briefed on any little foibles your son has......for example,my son cannot leave the house without first asking me "have I got everything mum?",he also has to be the last person out of the family to use the toilet before we go out anywhere.There are many more little rituals he has,far too many to list.
Many people don't realise how important these rituals are to a child with ASD (autistic spectrum disorder).
I recommend you buy a book called "Can I Tell You About Asperger Syndrome?" by Jude Welton and ask everyone who has any contact with your child (family,friends,teachers etc.) to read it. My son's first mainstream primary school bought several copies of it once I had shown it to them and they found it invaluable to both teachers and pupils.