Dry heat sterilization is fairly inefficient, time-wise, in general. According to Wikipedia, which cites the CDC for this:
The proper time and temperature for dry heat sterilization is 160 °C (320 °F) for 2 hours or 170 °C (340 °F) for 1 hour or in the case of High Velocity Hot Air sterilisers 190°C (375°F) for 6 to 12 minutes.
But this is for all mirco-organisms, which some of which are more hardy than coronaviruses. I'm not sure if there's a study just on the latter in re dry heat.
Also this is not exactly what you're asking here, as you want to sterilize the air, but it is somewhat relevant if you're trying to do that by heat transfer from a surface, e.g. a hot plate, coil etc. Because of inefficiency relative to other methods, this way of sterilizing air it might not have been studied too much, e.g.:
Many ways have been suggested for sterilizing air. These include destruction of microorganisms by: dry heat-gas fired or electrical; adiabatic compression; and irradiation or removal of microorganism. The removal of microorganisms involve: scrubbing, electrostatic precipitation, sieving, and filtration fibrous or granular beds. Of these, only adiabatic compression, filtration through beds of fibrous materials, and filtration through beds of granular materials have found widespread usage on an industrial scale.
(Albeit that's a 1960's article, but physics didn't change much since...)
The (1st) (2020) paper you've linked to uses a heated filter, so it's really a combination method. (The filter had non-zero effect even without it being heated, if you look at their graphs--fig 3.) That paper also mentions the air flow rate at which they've tested their system. Which of course is a factor in heat transfer too; e.g. they quantified the observed temperature drop with increased air flow, albeit only at couple of points.
See also sterility assurance level for what professionals mean when they say something is sterilized. Basically, it's a statistical measure/guarantee, not an absolute one. In the 2020 paper you've linked to, they set/measured that at 99.8%.