How to set timeout hours for workflow notifications.

Hi,

We have nearly 30 custom notification workflows for custom and standard.

We need to set timeout for these workflows.

For example --> one workflow have 3 level of approvals.

if 1st level approver is not taken any action from 48 hours once he received, the workflow will goes to 2nd level approver. and no time limit is required for final approver.

How to incorporate this changes in the existing workflows.

Regards,

Shiva.