Explanation:

To meet Universal Containers’ requirement for a case handling process where each case must progress through a series of steps within specified timeframes from submission to closure, defining entitlements and milestones is the most suitable solution.
Salesforce’s Entitlement Management allows administrators to define entitlements, which outline the support customers are entitled to, and milestones, which are time-based checkpoints for case progress (e.g., response, resolution). For example, milestones can enforce that a case moves from “New” to “In Progress” within 2 hours or is closed within 48 hours.
If a milestone deadline is at risk, alerts or escalations can be triggered. This aligns directly with UC’s need for a structured, time-bound process and integrates seamlessly with Service Cloud, as outlined in Salesforce’s Entitlement Management documentation and Trailhead module (Service Cloud Entitlement Management).
This solution ensures compliance with time-based steps without requiring custom development.

Why Other Options Are Incorrect:
Option B: Enable and configure Omni-Channel routing:
Omni-Channel routing assigns cases to agents based on availability, skills, or workload, optimizing case distribution. While it improves efficiency, it doesn’t enforce specific time-based steps or track case progression through a process, making it unsuitable for UC’s requirement, per Salesforce’s Omni-Channel Setup documentation.

Option C: Implement Lightning Flow with time-based actions:
Lightning Flow can automate processes with time-based actions (e.g., sending notifications after a delay). However, creating a custom flow to manage a multi-step, time-bound case process requires significant development and maintenance compared to the out-of-the-box Entitlement Management feature, which is purpose-built for this use case, as noted in Salesforce’s Flow Builder documentation.

References:
Trailhead: Service Cloud Entitlement Management
Salesforce Help: Entitlement Management Overview
Salesforce Help: Set Up Omni-Channel
Salesforce Help: Flow Builder Overview