Term of return the contract ensuring depends on the performance of the principal obligation

In the documentation for the purchase the customer must provide a period in which customed needs to return the funds pledged as contract ensuring. It should be to take into account the period of performance of the principal obligation (delivery of goods, works, services).
Analyzing the Economic Development Ministry explanation, you can draw the following conclusion. If the main obligation has been performed properly, customer may return the contract ensuring before the deadline.

Document: Letter of the Russian Ministry of Economic Development on 18.12.2015 N Д28и-3722