I have an intention to do a working to detach myself from a very negative former friend. I have done a forty day working in the past to try and do this. Maybe I did it wrong, or perhaps I didn't do it long enough. They are still very attached.

What I did last time was try to use munka to detach them. I've read the page on detaching people and entities, and if I did that it would tie up time that I use for my normal meditations.

I have a plan to use munka * 110 for 110 days with the affirmations of:
(I am cutting off all connections and ties from so and so to my soul
I am completely cutting off so and so from any and all sources of my energy and emotions
I am completely and totally free from so and so's interference with my life.) X 9

Would this munka approach work for what I'm trying to do? Or should I just stick to following removing people from the souls directions for at least three months and just deal with the time constraint?

Munka is the destroyer of karma, not relating to this. There is no need for a huge Munka working to remove a person, which is why it didn't work the first time. Also, you have convinced yourself you need 3 months to effectively do this, this mindset will make it take that long and/or just not work. When you start, KNOW that the person will be detached IMMEDIATELY, and it won't take long. 3 months is a ridiculous amount of time.

Just do the regular detaching, the one with THTHTH while visualizing an astral knife and Satanic fire removing the links. Do this daily starting after a full moon, 40 days max, but people have detached from people in much less time.

Also bind the person if need be, on the full moon on the 13/14th.

What Lydia said is really good and works but here is another one that will also help really quick especially if you have issues with visualization or focus you can do both if you want. I tested it on me and others and it works quite well from what I can tell.

Never used Munka to remove links though not sure that works for that this is probably why you had issues.

Vibrate Ansuz in a mutiple of 9 (nine is a number of finality or permanance from what I understand) into each Chakra then with each Chakra with focus and intent. Now say something like (you can create your own affirmation but I just want to give you an idea but the words now or right now should always be used as it seems to make it work much more quickly) "the energies of Ansuz are completely and eternally removing all connections and influences of ______(name of person) from my crown chakra right now" say it either 3 or 9 times (nine works much better) and while saying it visualize blue fire burning the whole chakra cutting away all links to that person. You may hear a little snap in your mind or something when the link is broken. Do this with the 7 main chakras and if you think there is some other link on your main body as well or wherever you feel it is.

This is the way I use to remove links I think both works.

This is personal adaptation of one of Hoodedcobras workings he posted about long ago btw. It works