SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21bf44af06877366b690201f4e338213aa7a7c4e9ffd984f53a01104883437bc' 
  AND token = 'JKmDcnlDBGuVw3SKZiMBlyTKRI552+VLmk+Mu7LlemQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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