This varies on the service that you are tapping from. For example, Twitter has norm of conducts for programmers which place limits in the number of requests per second(req/s) and daily quotas for requests. These limits are modest and for most people, they should not hit the limits unless you are pushing it. You need to know about these limits and design your application to take them into account. Note these limits depend on each site and hopefully they make it available to programmers (they should as it is to encourage best practices). If you cannot fin limits and quotas for services, you can email them.
As a developer/coder, the key point is to implement best practices in your code. Your code snippet is an excellent demonstration of a proper way to do it. At the end, it is very unlikely you want to send request at the same time as the refresh rate of your sketch. If that were the case, there are other techniques which falls under the domain of streaming.
Kf