SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '879fee4b7528d70e61f67a7122f1dfacc2c2663cdd1cacdd270b6a879111816a' 
  AND token = '3KSiGqCvA/x1RZgl+4GYfEmMNZDxB5NV8w00kVCEz9I=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}