Hello Lucas Peñaloza,
There is no "timer" or hard limit in the Windows Cluster itself. You can keep a node paused for days if you want. The real limit is the Free Disk Space on your Primary Node (PWGIRSQL1).
When you reboot PWGIRSQL2 for the OS upgrade, it stops communicating with the Primary. Because your Availability Group is active, PWGIRSQL1 cannot truncate or shrink its Transaction Log until it confirms that PWGIRSQL2 has received the data. As your users continue to write to the database, the log file on PWGIRSQL1 will grow continuously to hold those pending records. The Danger Zone: If the disk drive hosting the Transaction Log on Node 1 fills up (0 bytes free), your Production Database will stop working (freeze) immediately.
Before you start, perform this quick calculation:
Check Free Space: Look at the drive letter where your SQL Logs reside on PWGIRSQL1 (e.g., L: drive).
Estimate Growth Rate: Do you know how much log your database generates per hour? (e.g., 1 GB/hour?).
Calculate the Limit: Free Space / Growth Rate = Maximum Pause Time.
Example: If you have 100 GB free and your server generates 5 GB of logs per hour, you have 20 hours of safety. If you have 10 GB free and generate 5 GB per hour, you only have 2 hours.
Recommendations
Typical Window: An OS In-Place Upgrade + SQL Upgrade usually takes 1 to 2 hours per node. In most healthy environments, the log drive can easily handle 2 hours of growth.
Safety Valve: If the upgrade goes wrong and PWGIRSQL2 is offline for longer than expected (and the disk on Node 1 is filling up), your emergency move is to Remove the Availability Replica (PWGIRSQL2) from the Availability Group via SSMS on Node 1.
Effect: This tells Node 1 "Stop waiting for Node 2." The log will clear/truncate, and production is saved.
Downside: When you finally fix Node 2, you will have to re-seed the database (full sync) from scratch.
__In short, c__heck the disk space on PWGIRSQL1 now. If you have plenty of space (50GB+ is usually safe for a maintenance window unless you have massive transaction volume), you are safe to proceed with the update.
VP