SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c8b1428e38a0347815445f11397119656283ace4fb2f996b4b7e37c875916196' 
  AND token = 'NtF+Gqj3MyzefVLI8az0JyO+EYXqGZTL5XMBZyEl/G4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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