When should I expect to pay a call out charge?

Only after midnight in our case, which is £40

when you satisfy with the job

After the job complete why do you have problems paying for a job if so we could set up a payment plan

Every time , fuel and insurance costs money and you want engineers to be there with a full van of tools and spares which is a huge investment, at some point the customer must accept the cost and be as honest as the engineer who is coming. DONT EXPECT SOMETHING FOR NOTHING Its a bad habbit !!! theres no such thing, pay for a good service and you will get it.

I would say a call out charge should be made anytime after 6pm of £20 I would not charge one through daily working hours unless it was a distance and then I would only charge fuel costs. Craig CLW Plumbing Pontefract

Call out charges normally apply to "out of hours service" I.E outside of a normal working day and weekends. But it does depend on the policy of the company.
My core work times are 08:00 to 18:00 Monday to Friday, any time after that is what i consider to be call out. My week end call out times are Saturday midday to 08:00 Monday morning.
Depending on whereabouts in the country you are. you should expect to pay anywhere upwards from £45 for call out hourly rates.
Some companies charge a flat rate for the first 30 minutes and then increments of 30 minutes after that.
As a rule, if a tradesmen arrives at your property during core working hours, but, is still working after what is considered to be core working hours, then a call out fee should NOT be charged.
Again it is down to the policy of the company/tradesmen

only charged if out of hours call out or emergency

When you can afford to pay within reason. If it's a call out then you was not expecting it or expecting to pay an unexpected call out charge.

with most companies it can be in normal working hours and more after hours eg 8-5 would be so much, after 5 would be more, and weekends more also, after midnight expect to pay more again. But in most cases the call out charge could include the first hour but parts if any on top.

we charge for a call out which includes the 1st hours labour