SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a50d2dec897ddbee4e48debf023e53adae075bb3c8357a06e39dc5fe97e56e06' 
  AND token = '5kGQcQrlb/KqHh6UNnYp/kWNephihnQClYyft6ScagQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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