Challenge mode help

Hi!

I am new player, picked up Viper as she is the coolest (obviously).

I need some guidance on her Challange level 15
It should be:
cr lp
s lk
cr mp
ltk
EC

Now i can do 2 of them after one other, also i can do the first three | cr lp : s lk : cr mp | but i can not connect ltk, either it does not come out, or comes out too late and Dan blocks.
In my 3-4 hours of trying this i could connect the ltk around 3 times, but have no idea why was those different

thanks for any pointers