Depends on the context
Statutory timeframes
Certain documents, like a Statement of Claim or an Adjudication Application, set very strict timeframes in motion by their receipt and there are real legal consequences if they are not responded to within a statutorily mandated period. For the former, failure to respond may result in a default judgement and, for the latter, it prohibits the adjudicator from considering a response.
In such circumstances, the statute will set out the notice period.
Contractural timeframes
The document may be initiating an action where there are timeframes spelled out in a pre-existing contract. For example, what’s commonly called a “show cause notice” is a notice from one party to the other that they are invoking a contractural term that requires them to give the other party the opportunity to respond, that is, to “show cause”, why they should’t do something the contract then allows - like terminating it.
In such circumstances, the contract will set out the notice period or, if the contract is silent, then a reasonable notice period is required - see below.
Reasonable notice
It is inherent in contracts, but also a feature of the law more generally, that when a specific notice period is not given, reasonable notice is required.
What is reasonable depends on all the circumstances including the ability of the recipient to respond, the severity of the consequence of not responding, and the urgency of the issue. For example, a reasonable time to respond to an eviction notice will be longer than that required to respond to remove your vehicle that is blocking a fire escape - particularly if the building is presently on fire.
Date of the notice or date of receipt?
When measuring all these times, the question might arise as to whether they are from the date printed on the notice, the date the notice is delivered (or, in legal speak, served), or the date that it comes to the attention of the recipient.
Again, that will depend on the circumstances and a statute or contract may measure time from any of those things. They may also have deemed receipt, that is, receipt has legally occurred even if it hasn’t factually occurred. For example, receipt may be in the ordinary course of mail for a posted letter - so for a letter posted by Express Mail, the next business day after postage even if the Post Office loses it.
Any or all of these may be subject to their own measures of reasonableness. For example, even if the time is measured from the date on the notice, this would not be reasonable if the sending party waited 2 weeks before sending it. Similarly, if the recipient can demonstrate that they spent the last 6 months in a coma, it might not be reasonable to sanction them for failing to respond.
The legal art of service, deemed or otherwise, is a whole subsection of law in itself.