I don't think there's a one size fits all answer. Depends on the fruit & why you are spraying.
June for some like Plum moth, others, codling moth for instance, after blossom fall

Same for insecticides, but as times & regulations change so do recommendations.
Once I'd have said DDT now I tend to not spray unless I see the pest, such as sawfly, but my livelihood & existence does not depend on having fruit

Some swear by biological controls, I can't comment on effectiveness as never used them

Thank you for your help I will just watch out for any type of pest and deal with it then.

If the tree that you are talking about consistently has a particular problem every year, then you could do some preventative spraying or other treatments. Otherwise, spraying with general, non-biodegradable insecticides and fungicides 4 times a year is, thankfully, becoming a thing of the past. Organically speaking, a tree's first line of defense is is a diverse soil flora with plenty of earthworms, mycorrhizae, and other symbiotes, and moderate, slow acting feeding. Planting flowers near the trees, especially plants with small flowers in spikes, encourages beneficial insects to live in the vicinity.

I know this sounds unconventional but I have a wasp nest in one corner of my garden and those bad boys go to town on all those harmful insects. They do a good job and patrol the garden all day long. If you chose this method, never go outside barefoot and keep a box of epsom salt nearby. That's what you'll be soaking in if you get stung.

The paper wasps and assasin bugs go for the caterpillars amd other big bugs. Ladybirds, hover flies, lacewings, gnat-sized stingless wasps, pirate bugs, and many others go after the small bugs. Indiscriminate spraying easily kills all of these, while the pests rapidly become resistant--then you find yourself in pest purgatory, while the pollinators are dropping out of the sky.

Many thanks toTugbrethil,Grandad and Bathgate for your kind response I will try some of these ideas and hopefully get a good crop of fruit this year. Green 70

You're welcome. I've only been stung once when I stepped on a wasp barefoot in the grass. The pain was unreal