PM ledge dash (and ledge jump > WL) grounded actionable intangibility frames:
17 frames: Bowser*
14 frames: Fox, Olimar
13 frames: Squirtle, Ice Climbers
12 frames: Falco, Pikachu, Kirby, Sonic, Mario
11 frames: Luigi, MK
10 frames: Shiek, Wolf, Toon Link, ZSS, Ivysaur, Jiggs, Pit, ROB, Wario
9 frames: Lucario, Charizard, Zelda*
8 frames: Diddy, Roy, GW, Marth*, DK*, Peach*, Link
7 frames: Captain Falcon, Samus*, Ganon*
6 frames: Ike, Marth, Zelda, Mewtwo
5 frames: Snake
4 frames: Samus, Yoshi*, Ness*, Lucas, Lucas*
3 frames: DDD*, DK, Ganon
2 frames: Bowser, DDD
0 frames: Yoshi
-2 frames: Ness
-7 frames: Peach
Some characters names appear twice: once normally, and once with an * next to it. The fact that their name appears twice means that they possess a faster ledge jump > WL as opposed to a ledge dash (< 100% ledge jump, btw). When their names appear normally, without the *, it signifies the frame data of their normal ledge dash, whereas the * signifies the frame data of their < 100% ledge jump > WL. Characters like bowser are a huge outlier, and would have had a 2 frame ledge dash if done by the normal let go > jump > WL method, but instead he actually has the best frame data under 100% thanks to PM mechanics. This represents a big difference from melee, as ledge jumps in melee werent actionable until somewhere near the apex of the jump.
It seems that there are a number of factors that go into these numbers. character size, stage shape, vertical jump velocity, jump animation, and airdodge animation (thus affecting when you will collide with the floor) all look like things that affect a characters ability to quickly get off the ledge and make contact with the floor to gain as many actionable frames as possible. For instance, Roy inputs an air dodge on frame 17 (with frame 1 being when the ledge was first grabbed) and accquires 8 frames of actionable intangibility. On the other hand, Diddy needs to wait until frame 19 to air dodge, but his animations seem to let him land on stage earlier, and thus he also acquires 8 frames of actionable intangibility.
Also, these were tested in debug mode by attempting to WL on stage (FD) at the earliest possible frame out of a ledge hop (ledge drop on frame 9 after grabbing the edge, immediately jumping and holding towards the stage, WLing at the earliest possible frame, then holding shield, and counting intangibility frames once the shield appeared). The ledge jumps can occur on frame 7, so the same method was used (testing for earliest possible WL). Why the window is different for ledge jumps/rolls/get ups as opposed to simply ledge dropping is beyond me. there does exist the possibility that i may be off by a frame or two here and there, but these numbers represent actionable invincibility that I REPEATEDLY acquired in debug mode after several trials per character. thus, if there is any error, it is because there is some extremely specific level spacing/timing/tilting of control stick/ etc. that will allow the character to acquire maybe another frame of intangibility. for all practical purposes, this list can be considered a very good representation of a characters ledge dash ability.
edit:
Another thing to note is that Link only has 33 frame of intangibility upon grabbing the ledge, although he can ledge drop on frame 5 as opposed to everyone else being able to ledge drop on frame 9. another sort of oddball in the mix.
standardtoaster has made a great spreadsheet that should help quite a bit:
