Any change in estimated remaining useful life or revaluation / impairment is effective from the date that that re-assessment takes place
So, if estimated remaining life is re-assessed on 31 May and changed, that change is effective from ! June
The asset will be depreciated for 5 months at the previous rate and for the remaining 7 months at the revised rate
However, the probability is that, in real life, the re-assessment will take place officially as at the accounting reference date (ie the accounting year end date)