Entry date and pay date acceleration due to weekend/holiday

If this topic already exists, will happily take links (could not find in a few searches)... 

Employee enters the plan on the 1st of the month; payroll is typically run on the 1st of the month, but when it falls on a weekend or holiday, is paid the business day immediately preceding said weekend/holiday. Is the employee eligible to defer from that payroll?

My interpretation is no, since the actual pay date is before their entry date, but open to other interpretations / guidance here!

Example:

• Sally enters Company ABC 401(k) Plan on Sunday, October 1, 2023
• Company ABC follows a monthly pay schedule, with payment on the 1st of each month
• Pay date typically scheduled for October 1, 2023 is instead paid on Friday, September 29th due to the normally scheduled pay date falling on a weekend
• Is Sally eligible for deferral on the September 29th adjusted pay date, or must she wait for her first monthly payroll actually paid on/after October 1st (in this case Wednesday, November 1, 2023)?

I agree with your interpretation, in fact I think it's the only reasonable interpretation. Instead of 10/1, say we have someone who enters the plan on 1/1 - which is always a holiday. If they were allowed to defer from the previous paycheck, they would have contributions in the plan not just before their entry date, but actually in the prior plan year, which is problematic for lots of reasons.

Makes sense. The compensation was made available to the person on 9/29, a date before the effective date of participation which is the earliest date any salary deferral could be effective.