SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50e79c0061435b42f6dfb2d75842a0c9c977da2fe809f4dba2e2b750cea62708' 
  AND token = 'vHAoGbgYxTKgVsRSselrnYFBWXSLee+ThVnnvLMzKV8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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