Hi Vinny,
in your post 28 Days is pointing to following, here it is not specified that you need to enter in UK withing 28 Days:
Applying for settlement in the United Kingdom
This section explains how you can apply for permanent residence in the United Kingdom (we call this 'indefinite leave to remain').
After you have lived legally in the United Kingdom for a certain length of time (usually between two and five years), you may be able to apply to live here permanently, depending on the category of visa you have. You should see the appropriate category for more information on whether you can apply for permanent residence and the qualifying period for it. See Application types for details of categories that may qualify.
If your visa category is not listed in Application types, you may not be able to apply for permanent residence. If you are here on a working visa, the appropriate section of Working in the UK will tell you if it is possible to apply for permanent residence.
In order to apply for permanent residence, you will normally first need to show that you have enough knowledge of language and life in the United Kingdom.
You must not send us your application more than 28 days before the end of your qualifying period. If you do, we may refuse your application with no refund of the fee. However, you must make your application before your current permission to stay in the United Kingdom expires.
You can make a single payment to cover up to 25 postal applications by using form postal multiple payments, which you can download from the right side of this page. If you use this form, you do not need to to complete the payment details in the individual forms for which you are paying. There is no need to use this form if you are making a single payment for a number of premium-applications when you apply in person at one of our public enquiry offices. Personal cheques must have a valid cheque guarantee card that covers the full amount you are paying.
For information on which application form you will need to complete, see Application types.
Regards