Timeframe is one thing, monitoring frequency is another:
If the monitoring frequency is made equal to the timeframe there will not exist any monitoring during the journey to the desired future. You will have only one verification at the end, and if you fail to meet the objective it is too late to act. For example, in the picture above, before the end of the time frame there are three interim moments of monitoring allowing action if needed.
What is the best timeframe for an objective? It will depend on the dimension of the change needed and on the availability of resources.
The following material will provide you more information:
Free webinar on demand - Measurement, analysis, and improvement according to ISO 9001:2015 - https://advisera.com/9001academy/webinar/measurement-analysis-and-improvement-according-to-iso-9001-2015-free-webinar/-2015-free-webinar-on-demand/