(a) That's right. As regards the time of delivery of goods, there are provisions in the relevant sale of goods legislation saying that, if the time of delivery is not an agreed term of the contract, then delivery must take place within a reasonable time. See a list of the relevant sections.

What is a 'reasonable time'? This is something that must be judged in the circumstances of each case. In the present case, A seems to be taking longer than a reasonable time to deliver the wheat.

Performance within a reasonable time is generally required by law in all contracts if no time for performance is actually agreed.