Wow Apple my sympathies [sad} you must be feeling like you have been kicked by a mule.
To give you what amounts to 2 days by the time you take out the weekend & bank holiday to look through all that, talk to a union rep etc is unreasonable. What are they saying they are actually investigating you for? Or have they just said we are having a hearing and here is the backing paperwork?
What about the witness does she always start before you and leave after you? If not can you ask for copies of her times sheets so that you can cross check that she was there to witness you coming in late/leaving early and fraudulently recording it?
Are they saying that you were the person on the internet for all these reams of internet sites? What information does the data contain? Do it has a time/date, pc logged onto, your log in ID plus the full internet link?
If any of it is for the day of the week you don't work, how are they saying that was you accessing the internet?
If any of this is where they had you down as logged into 2 PCs at once, how can you have been browsing the internet on 2 PCs at the same time?
If you never went near PC 3 which they had you logged in on, how can you have been browsing on a PC you have never been on?
To be honest I don't really know how this work however if you look at someone on facebook doesn't it come up with a /some sort of profile ID on the end of the link. Can you have a look at these from your facebook and see who they relate to? Check out who they belong to, also if there are any updates in work time as you would not have been updating other people's profiles...
I think they are up shit creek with this 'evidence' as it soon falls apart with your working week and their logging authentication errors.
I do think that a trip to a lawyer would be useful now.
Stay strong and feel better soon.