If a checkbox

Hello again. 



I need some help please with automation/formula on a project management sheet we use. 



(Action 1) I have a checkbox column called "SNAGS"



When this is checked, I need a date column called "SNAG ADDED" to auto populate the date in which the checkbox was ticked by the project manager. 



(Action 2) Like wise, I have another checkbox column called "SNAG COMPLETE", I want another date column called "SNAG CLOSED" to auto populate with the day the checkbox was ticked



(Action 3) Next to the date columns "SNAG ADDED" and "SNAG COMPLETE.

I have a column "SNAG DAYS TAKEN". I need this to auto populate the number of days difference between the two columns, so we can see the number of days taken to close a snag our from it being raised to being closed. 



Appreciate explanations/ formulas in layman terms if possible. I'm based within the UK if this helps. 



Thanks in advance. 

Stuart 



****On a side note, Is it possible for text inputs from one sheet- to automatically replicate and copy onto another sheet without having to copy & paste or even enter the other sheet you'd like to mirror information onto?