Cooling-off period uner Tier 5 Charity Worker visa

[YuliaB]

Hi everyone!
My Tier 5 Charity worker visa expired in July 2019, and I would like to volunteer in the UK for another year. I was planning to return to the UK (if I'm granted a visa) in late August. However, one of the charities I applied to said I cannot start the application process with them before September.
Does anyone know if I can prepare all the docs I need for a visa application and submit them, say, in June-July? Or I am not allowed to submit the documents to the embassy (immigration office) before my cooling-off period expires? I thought cooling-off period meant 12 months outside the UK, and not 12 months before I can start the application process.
Some of my friends had to wait for 3-6 months for the answer from the immigration office..
Best regards,
Yulia