Can't really answer checking luggage overnight question with certainty, but the issues with overnight layovers has been covered in some other threads here. DL changed layover allowance late last year from 24 hours to 6 hours on revenue fares to Caribbean and Central America before a stopover is created. The new fare rules do allow for stopovers, but there is a $200 surcharge as can be seen in fare rules below. They briefly also applied these new stopover fare rules to award bookings, but relented and went back to allowing 24 hour layovers on award bookings before a stopover is created. For whatever reason, DL won't show these overnight layover options (with $200 stopover fee) on revenue fares. ITA Matrix will show them and you can bring them up on delta.com with ITA Matrix Powertools, but remember, there is a $200 fee surcharge built-in for these overnight revenue fares due to stopover. Stopover surcharge is embedded in base fare and not broken out.

DL multicity search was handicapped many years ago to require stopovers between each search term as it does not correctly check married segment inventory availability and can generate incorrect fare quotes when combining segments on a single fare component. However, it is still using old 24 hour layover limit for fares to Caribbean and Central American and won't price out anything unless you have at least 24 hours between flights to these destinations.







Here is the same VNXL0SBZ fare on BOS-AUA, but without $200 stopover fee as layover is less than 6 hours. Depending on fare pricing, it may be cheaper to book a one-way fare on BOS-JFK on it's own ticket and then JFK-AUA-BOS fares on another ticket rather than paying $200 stopover fee if you want an overnight layover on outbound.