Have you looked on your council's website? I did look on ours and it doesn't say when this must be paid by, but yours may.
Having said that I did find who was getting extra discretionary money.
This is my council - other will do it differently
The government has given us extra funds to support vulnerable households.
To support as many people as we can, we will provide:
£150 for households in bands E to H who are in receipt of council tax support or are exempt from council tax on health grounds
£100 for households in bands A to D who are in receipt of council tax support and have children living in the property