Personally, I ignore timing at idle speed in a car that is used for high performance.
Best bet is to time for max advance and let idle timing spec fall where it may (assuming the car will start and idle OK).
To do this, I guesstimate a max advance based on fuel available. Then I test for spark-knock (or detonation, or pinging or whatever you want to call it) and I adjust timning as needed. A good place to start for most cars is around 30 degrees of max timing advance, generally set at a fairly high rpm.
As it so happens, I have a mildly modified 1500 Spridget with 10:1 compression, Euro-cam specs, 2-1/8" race carb, mild port matching, header, etc.
On street fuel (93 octane RON), I am able to run around 26 to 28 degrees max advance (I set it at 5000 rpm). For race fuel (in my case, Sunoco GT 100 unleaded), the engine can tolerate a max advance of 32 degreees total.
The street Midget above would probably work out well if set for about 26 degrees max advance at 5000 rpm (on premium street fuel).
Obviously, you need a degree wheel or marks on the front timing pulley to measure this. I simply marked the front pulley from 24 to 36 degrees and use a non-adjustable timing light.
Again, this is in response to the needs of a car that is modified for perfomance and assumes the car running at relatively high rpms and hard acceleration.
For street cars, where smooth idling is important, low speed timing may be more important.
I haven't a clue where my timing is at idle speed.