If you do something from time to time, you do it occasionally, but not very often
Despite this meaning, the phrase from time to time is used slightly differently and in several contexts. First of all, it clarifies that an action is required or permitted more than once:
Customer may from time to time require Service Provider to provide it with a certificate of insurance.
Without the suffix from time to time, Customer may demand this certificate only once. The phrase permits Customer to request the certificate as many times as it likes. A second use of from time to time serves to clarify that the subject referred to may change after the agreement enters into force:
If Supplier desires to amend the Statement of Work, it shall notify Customer of all proposed amendments in accordance with Customer’s engineering change (EC) procedure from time to time.
Chairman means the chairman of the Non-Executive Board from time to time.
The examples bring aspects that may influence the object that is modified by the phrase from time to time outside the immediate scope of the provision. How and when the Chairman is appointed should be addressed elsewhere; it is clear who is referred to. Similarly, although a change in the engineering change procedure might well affect the possibility of amending the Statement of Work (or even render such amendment illusory), such change is outside the scope of this amendment provision