You don't have to hold ILR for 1 year.
The earliest you can apply is the date you meet the following residency criteria:
1) You were physically inside the UK exactly 3 years prior to your citizenship application date
2) You have not been outside the UK for more than 270 days in those 3 years, with no more than 90 of those days in the final 12 months.
If both of these apply on 22/04/2015, then you can apply on that date. If they don't, then you will have to wait until you do meet both requirements.
Basically, if you weren't in the UK on 31/03/2012, then you cannot apply on 31/03/2015.