Unlike other children, autistic children need a regular and consistent routine as it is very important for them to know what to expect and when to expect it. They look for consistency in their daily activities and are reassured by the fact that they know what will happen next.
Autistic children feel very uncomfortable with any changes in their schedule as well as with any other unexpected event. They do not like surprises and when these happen, they will not be able to handle it. In fact, anytime you change their schedule or their daily routine, you can almost always be guaranteed of dealing with a temper tantrum. This is because such changes push them out of their comfort zone. Keep in mind that consistency and predictability is very important for them.
It is also not enough that you verbally advise them of their daily routine. You also need to make sure that their daily routine is something that they can physically see. Since autistic children tend to think in terms of visual pictures and patterns, it would be a very good idea to create a schedule that they can touch, see and control. Show this schedule to them at the start of the day to remind them of the things that they will do for that day. This way, they are able to anticipate the things that they need to do. Having a physical schedule will also give them a sense of accomplishment as they are able to see the things that they have already done.
Another good practice is to indicate on the schedule how long each activity will last. You can even have a timer with you. Show this timer to the child and let him know when the activity starts and when the activity will end. If a particular activity is to be done for five minutes, having the timer will let the child see exactly how long five minutes will be.
If you feel that the child is not feeling his best or is feeling moody and irritable, do not hesitate to add more breaks as needed. Casually insert additional breaks into the schedule to give the child some time to rest in between. This will not only be beneficial for the child but for you as well.