Pokemon yellow route 1 to route 2 nido DSUM (Prolly bad lmao)
(Timebased DSUM following DSUM chart in Yellow Helper)
(Values in brackets are the start of the DSUM cycles if the encounter was met on route 2 (taken from yellow helper))

L3 Pidgeyx --> L3Rat 8(1i) outx
L4 Pidgey  --> L3Pid 6(9) out	
L2 Rattata --> L4Rat 8(7) out
L3 Rattata --> L4Nidom 10(5) out
L2 Pidgey  --> L4Nidof	11(4) out
L3 Pidgeyx --> L5Pid  1(3o) inx
L5 Pidgey  --> L6Nidom 2 in
L4 Rattata --> L6Nidof 1 out
L6 Pidgey  --> L7Pid 10(3i) out
L7 Pidgey  --> L7Pid 10(3i) out

As usual do 11 out 2 in or 2 in 11 out accordingly
(I'm bad at wording it but you should know what I mean lol)
Last tile of route 1 grass to old man battle	~+39s
Old man battle 				~+13s
old man to first grass on route 2		~+17s
from last tile to first tile should be roughly	~43s
similar to red the encounter slots for L3 Pidgey aren't really usable
Follow cycle of corresponding encounter
Look at the timer after encounter
From short testing, it seems to be pretty close with good shopping
But it definitely needs more testing and stuff

Edit: It seems to work with good execution :)
Here is a video Video that shows this DSUM with a L4 Rat encounter (Don't mind the dancing Tonys xd):
https://youtu.be/u6wGp9Fzy98