These are date fields, not text.

sql/supporters-schema.sql

@@ -53,8 +53,8 @@ DROP TABLE IF EXISTS "request_hold";
 CREATE TABLE "request_hold" (
     "id" integer NOT NULL PRIMARY KEY,
     "request_id" integer NOT NULL,
-    "hold_date" TEXT NOT NULL,
-    "release_date" TEXT,
+    "hold_date" date NOT NULL,
+    "release_date" date,
     "who" varchar(300) NOT NULL,
     "why" TEXT
 );