[SalesForce] How is calculated “24-hour period” for the limitation of Asynchronous Apex Executions

As per the link in your question, the following are not separate limits for the managed package, rather they're counted towards the whole org:

• The total heap size
• The maximum CPU time
• The maximum transaction execution time

Having said that, your DMLs inside the batch will have a separate limit for the managed package namespace, though the maximum CPU time for an example will stay the same for all apex in your org, regardless whether the code is executed withing the namespace of the managed package or your org in general.

So in regards to method executions, this link says that the maximum number of asynchronous Apex method executions falls into the Force.com Platform Apex Limits

"The limits in this table aren’t specific to an Apex transaction and are enforced by the Force.com platform."

Meaning that the governor limit will apply for the managed package as well.

Salesforce/apex does not support threads. There is no way to synchronize asynchronous apex. But if you want as a workaround, you can update some backend field in some object from the asynchronous apex and write a trigger on the object. Then using trigger you can continue remaining execution. It is not recommended.

Note - If you are okay to wait till asynchronous process is complete, use synchronous code instead of asynchronous(if you are not hitting governor limits).