If Maxibloom is a P and K additive for flower I would probably wait till flower.
I use Big Bud from Advanced Nute and I start adding it to flower day at 10% application rate and with each res change (every 10th day) I increase the doseage by 10% till week Day 40. So it looks like this.
Day 1-10...10%+flower nutes
Day 11-20...20%+flower nutes
Day 21-30...30%+flower nutes
Day 31-40...40%+flower nutes (here I have to reduce the flower nute dosage or TDS gets a little high and I risk burning my girls)
Day 41-50...No P K Boosters-just normal flower nute regimen
Day 51-56...Flush
For 63 day strains I do the same but flush Days 56-63
Hope that helps