questions about my plant

I have a bagseed that I put in the ground march 27th. It's ohh idk about 4-4 1/2 feet now and I topped it once at 3 feet. Anyways.. it seems to be growing good to me, but im a beginner so im going to walmart today to get some nutes, any special one that i should get thats good? also my plant JUST showed preflowers yesterday.. it gets sunlight from 5:00 am till about 7:00 pm. is there a certain amount of time from preflower till actual flowering and the creation of buds?

Try to find nutrients with a NPK ratio of around 1-3-2

yes you can switch to blooming nutes now or soon. take mollasses or syrup and mix two tablespoons with a two liter of water and water with that. the first time i did it my buds doubled in size over two days. results may vary lol