How soon before hitting the network are request hooks processed?

[austind]

I'm building an async client based on httpx for a service that uses request signing. Signatures must fall within a specific timestamp or risk 401 response. This is not a problem for low volume requests, but high volume requests run the risk of failing authentication due to sufficient clock skew (i.e., the request was signed >5min before it hit the network, as it was sitting in the connection pool waiting to be processed).

I thought a way around this might be using event hooks, and at first they seemed to work well. Though in at least one high volume test, I ran into a bunch of 401s. The docs aren't clear exactly when the request hook is processed, so I'm not sure what to make of it.

Are request hooks a good way to handle this? Any other thoughts appreciated!