CREATE TABLE public."RecordData"
(
  "id" uuid NOT NULL,
  "timestamp_start" TIMESTAMP WITHOUT TIME zone
)

WITH "expired" AS 
(
    SELECT "id" FROM "RecordData" WHERE "timestamp_start" <= '2020-10-16 11:45:00'
),
"fifo" AS 
( 
    SELECT "id" FROM "RecordData" ORDER BY "timestamp_start" LIMIT 50
)
 
SELECT "id", "timestamp_start" FROM "RecordData"
WHERE  "id" IN (SELECT * FROM "expired") 
OR     "id" IN (SELECT * FROM "fifo")
ORDER BY "timestamp_start"