I think your best bet is to just ignore namespaces and find the node by local name. You can do it with XPath like this:
node.select_single_node(".[local-name()='local-modification-time']")
Or you can just use C++ like this:
pugi::xml_node child_by_local_name(pugi::xml_node node, const char* name)
{
for (pugi::xml_node child = node.first_child(); child; child = child.next_sibling())
{
if (strcmp(child.name(), name) == 0)
return child;
const char* colon = strchr(child.name(), ':');
if (colon && strcmp(colon + 1, name) == 0)
return child;
}
return pugi::xml_node();
}