There are three journeys running in the SFMC org, one is with date based event as entry source for birthday and other two are with same date based event as entry sources.
All the journeys are entering with a delay of 1 day and emails are delivered after the end of the birthday.
Scheduled time is morning at 10 am. RE-ENTRY: Yearly
https://help.salesforce.com/articleView?id=000316705&language=en_US&type=1&mode=1
Time zone for date-based filters in Journey Builder
Description When you define an entry source based on 'Today' date criteria in Journey Builder, the timezone for 'Today' is based on server time (Central Standard Time or CST).
Resolution
This means that today's date (as per your time zone) may not match the date in CST. In this case, you may need to adjust your date-based filters accordingly.
This is a known limitation in Journey Builder, especially for the Date Based event. Where in you have to adjust your email Send time with respect to Central Time zone.
Below articles might help you to understand this.
Solution: set 1 day prior their Birth Date.
KNOWLEDGE ARTICLE: https://help.salesforce.com/articleView?language=en_US&type=1&mode=1&id=000316705
https://success.salesforce.com/ideaView?id=0873A000000cNueQAE
