Index: trunk/data/validator/numeric.mapcss
===================================================================
--- trunk/data/validator/numeric.mapcss	(revision 14593)
+++ trunk/data/validator/numeric.mapcss	(revision 14728)
@@ -349,2 +349,14 @@
   throwError: tr("unusual value of {0}", "{0.key}");
 }
+
+*[interval][interval !~ /^([0-9][0-9]?|[0-9][0-9]:[0-5][0-9](:[0-9][0-9])?)$/] {
+  throwWarning: tr("unusual value of {0}", "{0.key}");
+  assertNoMatch: "way interval=5";
+  assertNoMatch: "way interval=20";
+  assertNoMatch: "way interval=00:05";
+  assertNoMatch: "way interval=00:05:00";
+  assertNoMatch: "way interval=03:00:00";
+  assertMatch: "way interval=123";
+  assertMatch: "way interval=0:5:0";
+  assertMatch: "way interval=00:65:00";
+}