There are two settings within your marketplace that impact session duration, both of which are found in Settings > Security.
When enabled, this setting requires users to re-authenticate when accessing screens where they can perform sensitive actions such as deleting their own account or changing their primary email address.
The default period of time that a user can leave and return to a sensitive screen and not be required to re-authenticate is 60 seconds. When set to 0 (zero), users must always re-authenticate.
Increase this field by as much as you like to remain logged-in for longer periods.
Session timeout (Company Admins)
This field allows you to define the number of minutes after which a timeout occurs for Company Administrators, such as Marketplace Managers. If you do not change the setting, the 30-minute default value applies.