Hi
Your builder cannot take umbrage under the clause grace period and deny to pay you compensation citing grace period.
Grace period is applicable only in the event of force-majeure ( Standard clause found in construction and supply contracts, it exempts the contracting parties from fulfilling their contractual obligations for causes that could not be anticipated and/or are beyond their control. These causes usually include act of God, act of man, act of parliament, and other impersonal events or occurrences).
Based on our experience in handling cases at National Consumer Dispute Redressal commission, we can confidently state that in your case, the builder is liable to pay compensation for every day of delay commencing from April 30, 2017 and cannot claim umbrage under the grace period clause.
Hope this information is useful.