Willo hold
 

Looking at the AIP, the reason seems to be because of the different type of arrival. For a standard arrival or procedural approach the limiting DME is there. However the charts that don't mention it are the "new" RNAV 1 arrivals, which would make sense.

If you are flying a "standard" arrival v "Rnav 1" arrival, there is not likely to be consistency as they are different sorts of arrival and the same waypoint will be depicted differently. I guess you haven't flown to many German airfields where quite often the same SID designator can be RNAV or conventional.

Basically I use the hold on the chart that I am using for arrival....if its an RNAV 1 arrival I don't use the 5.1d limit (as the chart does not have it and the hold should be flown more accurately), and if I am using the standard arrival and the chart say 5.1d I use that.

Just put it in the box, check it looks right and then fly it. :}

Aircraft holding patterns used to be quite varied, less so now. But unless you're going way outside what's normally observed, ATC won't likely care or challenge.
Way back when, there were several aircraft going around the DAYNE hold waiting to approach MAN and in a quiet moment a "Nigelesque" voice asks "Approach, this is 2 November, the chap below us, what hold is he flying?"

Tubby,
The wisdom of my ATCO son and his wife ( the grumpy antipodean! ) with 30 years experience of that sector between them is:- ATCOs don't care as long as you stay in the holding pattern!

Holds in the UK are 90 second legs unless otherwise specified on the hold chart, I'll try and find the official link to where that is written.......

It says on the approach chart here in the general information, point 5, the hold is limited to MID VOR at DME 22nm, so I'd say that means this one isn't timed legs, but this is just the RNAV-5 arrival and the equivalent RNAV-1 STAR doesn't have anything mentioned on the chart so I'd say this one is a bit "muddy".

Found the enroute holding document in the AIP here that lists all the established enroute holds and whether they are 1 minute, 1.5 minute or distance based legs, but as WILLO is an approach hold is isn't included.

Pretty much sums it up ;)

TBH I think the 22d MID is a limit to stop pre FMGC aircraft drifting towards the TIMBA hold.

As I mentioned in a previous post.........at LGW, if the STAR is a standard STAR it will have the 5.1 dme limit. If it is the "new" RNAV arrival it won't mention DME limits because they expect an RNAV 1 aircraft to stay within the protected area with a 1 minute hold.