I have seen people using
Runtime and designtime for a computer program.
Is designtime a valid word?
Germanic languages often form compound words like designtime, so the meaning is readily understandable. As a matter of convention, however, English writers typically write them as separate words except for very common compounds:
This Ngram shows that the compound word designtime has become more common in the last 20 years, although writers still prefer the phrase design time by about 30 to 1. Therefore, while it's reasonable to use the single word in parallel with runtime, it's not preferred usage.