DHCP and, to some extent, IPv6 addressing is on a client-driven basis. There isn't a real push mechanism for "ignore what I told you before, you should use this lease".
Note that an IA_PD has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the prefixes in a IA_PD
have expired, the IA_PD can be considered as having expired. T1 and
T2 are included to give delegating routers explicit control over when
a requesting router should contact the delegating router about a
specific IA_PD.
Setting a short time for the leases you provide can help speed the process. I typically use a 600- or 900-second period, so that clients typically "check in" at 5 or 7 minutes, and all should have picked up the new assignment within 10-15 minutes.
Some related threads that might have other suggestions include