72 or even 48hrs should be easily enough for you to arrange a companion or guide perhaps this website will help find fellow moles or follow the links page
Try to decide which caving area are you intent upon?.
Are you thinking of buying or hiring the required equipment? if so, are you aware of the right equipment to buy/hire, as this may vary depending upon venue.
As said above there are usually people that would be able to guide you or allow you to tag along with them at the drop of a hat, clubs will provide you with loan kit free why spend hundreds of pounds on kit you may never use again, if you wanted to hire all the required kit, you may only have the option of one or two suppliers. thus limiting your caving area.
If you are serious and want to cave there are many pleasure cavers that may be able help and also paid cave guides whom would be able to help well within your time scale.
There are other problems associated with various different types of mines and even some so called "safe" mines have recently become unsafe due to unknown factors like L.R. where some explorers were very lucky to escape with their lives.
You may stumble upon, false floors, lack of oxygen, toxic gas, roof / tunnel collapse just to mention a few, they are often a labyrinth that would have you lost and exhausted.
Caves & mines may appear secretive lonesome places, but as for a hiding place they would be the last place I would use, far to much through traffic, often busier than my local pub, that is not to say you would be found in time to save your life if you were in difficulties
Hypothermia, and exhaustion can easily take down a fit man in a very short time, as for "Dangerous sports" I know several superb hard high grade climbers that would not stand a snowball in hells chance on their own in a cave / mine.(no disrespect to climbers here, just illustrating my point)
We do get great cavers who climb and the other way around, but it certainly does not infer that proficiency in one automatically mean that one will be proficient in the other.
Caving is caving not climbing or abseiling it has huge differences, and to be cave fit is no easy task, only last week I took a group of cavers, fit healthy young men all of whom had caved for some time, around an "easy" cave, by the emails I received that evening, they would not have managed another couple of hours without difficulties, including myself. I generally cave 1 or 2 times a week, often more.
I also think solo caving is legitimate and rewarding, however with extreme caution and much experience, I would recommend you get a few years and many caves , experience under your belt before trying it.
As mentioned above DCRO CRO call outs pages are a wealth of useful information, and I cant think of anyone whom has not nearly killed or injured themselves once or twice myself included.
Ron