You can have a clearance any time before the wheels touch the runway. In countries where the clearance cannot be issued until the runway is actually available (as opposed to there being a reasonable assurance that it will be) this can mean clearances regularly issued at half a mile on a nice day.
If the weather is poor it gets more tricky but the key is to make sure that everyone knows what is going on. I can clearly remember a handful of times when a big aircraft was in the flare before it got a clearance (or on another occasion that I clearly recall, had to go-around). Likewise I recall seeing a very impressive go-around by a 737 because they mis-tuned the TWR frequency and couldn't make contact by the time they were over the numbers. All this - and similar - stuff happens on a daily basis and if handled in a suitable way (although undesirable) should surely not be considered anything special.
For ILS and visual approaches the ICAO book (Doc 4444) gives no minimum distance - for radar approaches there are procedures which should ensure that a landing clearance (or whatever) is issued by the time the aircraft gets to 2NM.