Unhide rows based on semi static, semi dynamic value

Hello again excel ninjas!

I have this code

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Which hides rows, based on phone call durations shorter than 600 seconds (a value stored in column N).

Now I want to UNHIDE phone calls made to certain phone numbers, regardless of length. Specifically, any phone call starting with 13 I want to unhide, but sometimes they'll be 13#### and sometimes 13########. This information would be found in column K

Basically what I'm struggling with is how to specify the dynamic criteria in VBA?

Saving my bacon once more! you're a champion Hahobe!

As for the on error line, it had previously been throwing out a weird error, when the code looked very different. I've changed the code since then and been lazy and left that in. Now the code runs perfectly, I'll get rid of it thanks for helping me keep my code clean!

One final question:

This runs on 305 unique worksheets. it takes *forever*. Anything I can do to speed it up? turn off screen updating? tilt the computer so the electricty can run down hill? sacrifice a goat? :P