The planned opening of the primary and secondary schools, in the Castel, has already been delayed by a year and is now scheduled for September 2018.
Chief Minister Jonathan Le Tocq said putting the decision back by a month would not cause further delays.
He said the time would be used to ensure points raised had been answered.
Deputy Le Tocq said the Policy Council had only had the chance to discuss three elements - the Education Department's report, the Treasury and Resources Department's comment and the independent review panel's report - on Monday.
He said: "Having discussed all three, I will be actively encouraging both the Education and the Treasury and Resources Departments to address points raised, in order to ensure we demonstrate a balance between the needs of our community's education system and best value-for-money for taxpayers."
The plans include an autism centre and improved sports facilities.
The secondary school is the last of the States high schools to be redeveloped, following the rebuild of Les Beaucamps and St Sampson's.
A final decision on the £59m redevelopment of La Mare de Carteret schools will not now be made until May, Guernsey's Policy Council has ruled.