Agree with Anil, the suggestion is to first start with Process Mining and understand what is happening in the process in the system. If a majority of process happens to be done manually outside the system, then including Task Mining is the next right step.
In Process Mining, you use data from system of records like SAP or Salesforce, so it is not about a single run or few hours of capture, but you extract logs for last few months. The general suggestion is to start with one month or one quarter of data first. You can ingest more historical data later.
In terms of the process as well, the recommendation is to start with a small section of the overall process and expand focus as you make progress.