[SalesForce] Session Settings

Sessions expire after the specified amount of idle time (see below), rather than an absolute time period. So, assuming your session timeout is at least an hour, you will keep it active by making a call every hour.

I wouldn't rely on this behavior for the long term, though. If the org admin reduces the session timeout, you will find your batch job failing. A more robust solution would be to do OAuth, keep the refresh token, and exchange it for an access token (aka session id) every hour (simpler) or whenever you get a session expired response (more efficient, but more complex).

The actual session timeout behavior, from the docs:

The last active session time value isn’t updated until halfway through the timeout period. That is, if you have a 30 minute timeout, the system won’t check for activity until 15 minutes have passed. For example, assume you have a 30 minute timeout value. If you update a record after 10 minutes, the last active session time value won’t be updated because there was no activity after 15 minutes. You’ll be logged out in 20 more minutes (30 minutes total) because the last active session time wasn’t updated. Suppose you update a record after 20 minutes. That’s five minutes after the last active session time is checked, so your timeout resets and you have another 30 minutes before being logged out, for a total of 50 minutes.

At this stage I think the answer is: No, you can't bypass the "Lock sessions to the IP from which they originated" setting. Having this on essentially disables apps that integrate back into Salesforce using the current users Session Id.

The app would need to establish a separate session using OAuth or stored credentials.

Vote for the Idea: Lock Session Ids - Allow Trusted Networks Access

I'd be more than happy to be proved wrong here.