Docs

https://openwrt.org/docs/guide-user/base-system/dhcp_configuration

Static

/etc/config/dhcp

Luci

uci

uci show | grep dhcp | grep host

uci add dhcp host         # will create `dhcp.@host[INDEX]=host`
uci set dhcp.@host[-1].ITEM # -1 : last | -x: xth from last

uci delete dhcp.@host[-1]

uci commit dhcp         # refresh Luci
service dnsmasq restart # reconnect client

Lease Time

cat /tmp/dhcp.leases

uci show | grep dhcp | grep lease
=> dhcp.lan.leasetime='12h'

uci set dhcp.lan.leasetime='10m'
uci commit dhcp; service odhcpd restart ; service dnsmasq restart

per client

https://openwrt.org/docs/guide-user/dhcp/dhcp_configuration#dhcp_pools

luci: http://wrt.lan/cgi-bin/luci/admin/network/dhcp