Not necessarily a HE created issue,... and yet...
On a Samsung S6, S9+, S10 etc. that I've tested when setting up a RM to be triggered at a Sunset -60, I can't get a (-). Maybe there's a way, but I can't figure it out... all I get is the number pad for the entry, which doesn't include any operators.
resolved for me as I also have pc's, but if there's a way to do it on the phone it'd be nice to hear.
Galaxy S10 here...you don't get this number pad w/ the "-" negative/dash option? I'm using the Google keyboard - changed back to the Samsung and there are no operators there. And below only offers the - and not the +.
I have to temporarily change my phone keyboard to do the -
Yup, and looks like the + is just not available on Google or the Samsung numeric keyboard. @bikesquid has something here...
Yup, tried long-press on all of the keys, no joy. On both the Google numeric keyboard and the Samsung numeric keyboard.
You don't need a plus or positive sign. You're not writing an equation. You're just giving a value for an offset to be added. Any value without a negative sign is positive.
LOL...damn, are you a math PhD!?! 
[Goes off to brew another cup of coffee]
Thanks for waking up my brain. I'll be too busy to reply to any more posts for a while, will be spending an hour in the "Corner of shame." 
However, still an issue that the stock Samsung keyboard doesn't even offer a "-" option. Folks will have to use a PC or switch keyboards on their phone.
Not a PhD
But a measurements scientist(metrologist NOT metEOroligist). So, math is an integral part of my daily routine.
I stand corrected/shamed, and will always remember "Metrologist" from this day forward.
For some reason the bit from the delightful short "Ask Dr. Science" series that NPR used to play popped into my head...
Dr. Science: "Hi, I'm Dr. Science!"
Host: "He's not a real doctor."
Dr. Science: "I have a masters degree...in science!"
Well I'm just a Metallurgist, not a Meteorologist or a Metrologist and I still think a user interface should be as dolt proof as possible so minimally educated dolts like me can turn the damn lights on an hour before sunset!! 
Thanks for the keyboard swap suggestion... something to keep in mind for the future!
Or as we call it in my house, "Mom-proof."
[Grinning and ducking and running...]
Definitely not shaming.... LOL I just almost always get a question about the weather when I mention "metrologist"..... So, I have learned to head that off at the pass. 
I get it...you only do the weather for the metro area. Cool.
Close enough......
Download the Hubitat app
