Update note about the first 4.x LTS

The release date is yet to be determined, to allow time for 4.x to
stabilise.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/BRANCHES.md b/BRANCHES.md
index 93bcbbd..82f1894 100644
--- a/BRANCHES.md
+++ b/BRANCHES.md
@@ -26,8 +26,9 @@
 
 We will make regular LTS releases on an 18-month cycle, each of which will have
 a 3 year support lifetime. On this basis, 3.6 LTS (released March 2024) will be
-supported until March 2027. The next LTS release will be a 4.x release, which is
-planned for September 2025.
+supported until March 2027. The next LTS release will be a 4.x release. Due to
+the size and scope of the 4.0 release, the release date of the first 4.x LTS is
+yet to be determined.
 
 ## Backwards Compatibility for application code