Different nutrient company

Totally fine to start using em when ever you wish. No need to flush if switching brands either, so start using your new nutes asap if u want to. but with new nutes, always start on the weak end of the nute mix and see how plant responds over the following week or so. It takes time to see the changes from a new nute mix, 4 days at a minimum for synthetic nutes and much longer for organics, so start off weak and see how plant goes. Thats why people become so loyal to a brand they know works, they have dialed it in over time to get the mix right and dont want to change and do it all over again. However now with the net we can share info so the whole loyal to the brand mentality has to shift too. Try lots, see whats out there and dont just trust big names ok. Look at my nutes in my blue gorilla grow... I use all of em at diff times or on diff plants and as long as I dont mix them all together, I dont have issues using diff brands on the same plants. A week apart is more than enough time.