Even with 20+ years of development experience, Monday mornings are hard...

gistfile1.txt

object newValueInType = newValue;
string newValueAsString = newValue as string;
if(type == typeof(DateTimeOffset))
{
	newValueInType = DateTimeOffset.Parse(newValueAsString);
}
if(type == typeof(Guid))
{
	newValueInType = Guid.Parse(newValueAsString);
}
if(type == typeof(TimeSpan))
{
	newValueInType = TimeSpan.Parse(newValueAsString);
}
else
{
	newValueInType = Convert.ChangeType(newValue, type);
}
_defaultsPerType[type] = newValueInType;

Cant agree more with you about Monday.