My partner and I have recently had a baby together. Were now on about me adopting her child, We were wondering do we have to be together for a period in order for me to be able to adopt her child. We have heard it is meant to be 4 years, How ever we can't find anything online saying what the length is if there is one?

First, ANY question on law needs to include your general locale as laws vary by area.

Second, you were somewhat cryptic in your description of this relationship. We need to understand it more completely to help.

For example, you state you had baby "together", then ask about you adopting. If you are the biological father then you don't need to adopt, you simply need to sign an acknowledgment of paternity according to local laws.

We are currently living together. The child I wish to adopt is from my partners previous relationship. We now have a child together. And will be registering our child in a few days.

Again, ANY question on law needs to include your general locale as laws vary by area.

In most places, you need to be married, generally for at least a year, to adopt a step child. You will also need the consent of the biological father or at least show a good faith attempt to get it.

Myself and my partner are living together. We have been talking about myself adopting her child from her first relationship. How long do I have to be in a relationship with my partner until I'm able to adopt her child from her previous relationship?

Did you read what I last posted?

Sorry were in the u.k

OK, that helps. I couldn't find any specific time frame for the length of the partnership. This site:
Adopting a stepchild : Directgov - Parents seems to have a lot of good info about the requirements and process.

Since you have to contact your council in any case, they should be able to tell you specific requirements.