SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39600ce98261ddbc6b892cded62f5781a0d08b9c201988afb0a8a725d73b3138' 
  AND token = '2MQepvO7m3NfGmByJ3i7mVC93sxqM8wmCK5CUphNN1o=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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