SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5250bcc4480343aeba8f07131e2261bb9e9efb3f4d9595daaf6802b6dfbd62ba' 
  AND token = 'rcnVpDbaINkf08sKtBWiXR0F16dHpKaSkgoENtuGsSI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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