SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'cf76e1f9dc604c5ca8277bfce068de953c568b33b0a980b07aee2ae2f38be004' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}