SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '921ac1499138fec5ff47a0e4736302498a138eb1778d5aeee5e28b5270b1409a' 
  AND token = 'gsjUYdxCgZT+pSNSyhvYVSPTCZrzeuGJ4OrrpexlMrQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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