too late to prune cherry?

Hi Hedgehogg you say branches snapped off depends where they snapped. If they snapped close to main trunk then likely to have pulled a heel or sliver of bark away.If branches snapped then exposed end will have died back though side shoots may well be returning. generally it is recommended to prune late summer.
Surprised you read March as surely you would be removing that years blossom and fruiting cycle.
March is supposed to be early spring when sap is rising in trees.Pruning then would leave pruning sites weeping sap not a good idea with cherries as this when most likely to become infected.
This why late summer prune advised as sap has stopped then.
Would treat any open areas with tree paint seals wounds and comes with brush available most garden centres. Do not prune till August.

thanks very much for your reply i was also very surprised to read that cherries should be pruned in march but the book I bought called fruit expert certainly says prune young cherry trees in march. Like you say i was worried that i may remove this years blossom and fruit cycle. Sap is rising as buds are sticky. Maybe i will leave it to august like you suggest to be safe. Thanks for that

you can prune in March, but only remove the top part of branch past where the buds are !