decapeptyl for 11 years old boy

Hello,

I saw that you cannot read/write in hebrew, so I am writting in english. Please excuse my poor spelling and grammer.

My son's doctor recommand us to start injecting decapeptyl every 28 days.

We plan to go for a vacation and it means that the third injection will be after 29 days.

My question is how important is it to keep the percise 28 days gap.

Thank you