So you are concerned they won't complete the work on Oct3 and it might continue another two days?
I don't know if anyone knows what exactly they are doing then and so it might be hard to predict, but you could check back when the date is closer and see if there is more information available then.
Not really worried about being completed. From what Im reading it seems as if they are only doing work on certain days, but anything can go wrong at any time to cause a delay. Here is the text from Amtrak.
"Track Work Affects Texas Eagle Trains 21/421 and 22
Effective Select Mondays and Wednesdays April 24 - October 4, 2023
Due to track work being performed by Union Pacific, schedule changes impact Texas Eagle Trains 21/421 and 22 on select Mondays and Wednesdays, April 24 through October 4, as outlined below. Schedule times listed on Amtrak.com have been updated to reflect these changes.
April 23, June 27, September 10, and October 3
Train 21, which normally operates between Chicago and San Antonio, will terminate at Fort Worth, with alternate transportation provided via Bus 3021 between Fort Worth and San Antonio, making all intermediate stops.
Train 421, which normally operates between Chicago and Los Angeles, will originate at San Antonio.
April 24, June 28, September 11, and October 4
Train 22, which normally operates between San Antonio and Chicago, will originate at Fort Worth, with alternate transportation provided via Bus 3022 between San Antonio and Fort Worth, making all intermediate stops."