Mash on at 1635 Boil start at 6.30pm Hops in at 6.40pm (50 min) Hops in again at 7.15 and 7.25pm Off at 7.30pm
Based on boiling 24.60 gallonsliters at 1.032 for 60 minutes, this will decrease your wort by 6.00 gallonsliters, bringing your after boil OG to 1.040. You wanted an OG of 1.051. It looks like it will be under.