My manager is available on Tuesday, Wednesday, and Thursday after 12 PM PST and her manager is available on Wednesday after 4:30 PM CST and Thursday from 3:30 PM to 4:30 PM CST. Can you suggest a time for me to schedule a meeting with the two of them if I have to sign off at 5 PM EST every day?

Your manager is available after 3 PM EST but her manager is only available on Wednesday after 5:30 PM EST or Thursday from 4:30 PM to 5:30 PM EST.

The only time that the three of you are able to meet is on Thursday at 4:30 PM EST. If you can be available after 5 PM EST then all three of you are also available to meet on Wednesday at 5:30 PM EST or Thursday at 5 PM EST.