From the specification you will need to create a workflow with multiple approver blocks, instead of just one pointing to a group in a single block.
An immediate workaround could be defined as follows, using the current “Contact group” object:
1. add a new field on the employee record, which will designate which Group will be responsible for approvers on requests from this employee. This will be the first level approval.
2. Add another field on the employee record, designate a second level off approver, selecting another contact group
3. In your Service request workflow, let it send the approval to the fist group as per the logged in employee settings in (1)
a. If the SR times out, let it go to the next approval block for second approvers as defined in (2)
This will by far the easiest way to configure it.
Remember each contact group can have multiple approvers, meaning the groups will never change in names, just the approvers linked to the group. You will need to set the correct first level and second levels on the employees to allow the process to work though.
There could be other ways, the above is just the easiest for a multi-tier approval process with a fail safe. I wouldn’t recommend setting the fields to individuals, since then you need to manage the employees as the approvers change. Using just groups those are managed centrally.
Lastly, each approver block in the workflow could use the contact groups which have multiple employees linked to them by default. You are able to set the approver criteria, for example, if 50% of them approve it is approved etc. Using the mechanism above you will have multi layers of this.