I usually give the engine a good blast with an airline, this gets rid of all the loose debris. Then some Meguires apc worked in with a brush once its pretty clean i mop all that up with a clean rag then give the engine bay plastics a coat of autoglym vinyl and rubber protector or 303 and buff it off i then coat the metal work with a friendly silicone spray and re wipe, Job done
It usually takes me 4 ish hours on the first engine bay clean, but on its yearly top up clean it will probably on take 1 hour