The most obvious way that most of us here would do is to:

1/read the specs
2/get sample code (or write it ourselves)
3/count cycles
4/insert delays

So, if you've got code that works on a standard 8051, figure out how much faster your micro is and multiply the delays. Job done!

You didn't tell us what variant you're using as it could be a 12,6,2 or 1 clock part - this is critical in terms of time delays!