I think you can get the cDNA at -20 hold it for long. Even at -80 RNA remains too long.cDNA is in fact a double-stranded DNA to RNA is not sensitive.cDNA synthesis few months ago I got the result I'm keeping in -20 temperatures.
cDNA can be stored for years in -20°C. But for proper qPCR results I usually try not to store it longer than several weeks. But if you work properly during cDNA synthesis using nuclease free tubes, tips and buffers there is no problem in storing it for a longer time.
RNA always should be stored in -80°C, for storage of genomic DNA I usually choose 4°C to avoid induction of breaks in the DNA.