Rapid Connect is a setting to allow for faster address assignments for connecting clients and is included in DNSMasq. Just add option rapidcommit '1' to /etc/config/dhcp to enable.
This is especially noticeable with multiple AP's in which clients connect/reconnect frequently.
The client obtains the IP and configuration information in a 2-message exchange (Solicit and Reply) instead of the normal 4-message exchange (Solicit, Advertise, Request, and Reply).
This is only for DHCPv4 and doesn't affect DHCPv6 and only should be enabled if either the DHCP server is the only server for the subnet, or multiple servers are present and they each commit a binding for all clients.
The option wasn't in the list of options so I just added it.
I've enabled it everywhere and have had no issues.