Yes.. every transaction has a timestamp (created_at field).
Getting the balance is not pretty at the moment but can be accomplished as follows:
First specify your date range:
time_range = (Time.now.midnight - 30.days)..Time.now.midnight
Get the debit and credit balances via query:
Plutus::Asset.joins(:debit_transactions).where(:name => "Cash", :plutus_transactions => {:created_at => time_range}).sum(:amount)
Plutus::Asset.joins(:credit_transactions).where(:name => "Cash", :plutus_transactions => {:created_at => time_range}).sum(:amount)