As per this developer document:
As worker threads become available to process your Bulk API jobs, Salesforce assigns them to process specific batches.
This point is emphasised further in this Salesforce Developers video about managing large data volumes. Because of the multitenant architecture, the performance of the server that your org is hosted on won't be static.
Is there any information we have to identify the most optimum time to process a large batch job asap (i.e - not to use the scheduled batch job on a weekend)?
The best option I see is https://status.salesforce.com/status but this doesn't display any information about how many threads are being processed across a server, how many requests are in extended delays, or any information about the request lifecycle of a server.