How long till court-order lapses?

[dunfightin]

Court order is the regular wow and one evening after school in the week, plus holidays.
Ex is extremely flaky i.e. has disappeared for a month or more at a time, reappeared only to disappear again. This has gone on for the past couple of years at least and some bits of the court order he never does i.e. spending time with them on their birthdays.

I always make DCs available - hard to keep track of which week is which when ex does appear. After school contact is more difficult as I'm working the day he is supposed to have them after school. I've got a good friend who'll step in if needed and I get someone to text if the ex appears for school pickup. But it's getting ridiculous, ex tells the DC he won't be around but increasingly doesn't tell me or lets me know that morning.
So how long does this have to go on before I make a better more stable arrangement i.e. childminder for mid-week and also stop having to work around idea that DC may or may not be here or there on a particular weekend.
Ex is extremely difficult, won't communicate or is abusive and we spent months and months in and out of court sorting things like residence, holidays, me taking DCs out of the country, doesn't take DCs to any parties etc and I'm always having to second guess. And whole situation is awful for DCs as they never know who will pick them up mid-week and when they will see other parent or not. Mediation has been tried several times to which he won't go and I did used to get exemption due to abuse and previous failed attempts.d
Do I apply to court again? How long do I have to wait to say this isn't working or basically isn't happening. I've got evidence of it being very flaky since June with gaps of a month or more . It's taken DCs phoning and sobbing to get him to reappear.

[MrsBertBibby]

Child arrangements orders remain in force until each child's 16th birthday, or until a new order is made.

To change it you need to apply for a variation. Which will no doubt bring him along to court saying it's all your fault and he wants more contact, poor him.

How old are the kids?

[dunfightin]

They are both primary school. I can imagine that might be part of what he's up to.
So I let it lie and just wait until he turns up or not? I can't face more court, but if it's worth it any idea of how long I wait until he doesn't show up until I go for a variation? Six months? A year?
It's not that I want to stop contact, but it's impossible to plan around this and am continually vaguely anxious midweek until I know whether to ask friend to have them or not. I don't think I can keep on relying on her to step in as it also affects her plans with her DD that afternoon