I don't know if this was mentioned here or not, but Reisen's bomb actually does have one certain time limit, and it is the end of the stage, as it doesn't seem to pass between stages.
Dem glitches though... the only one I encountered was the stage 2 boss hitbox glitch. I was really surprised when I looked up on the screen for a second, and there was a giant hitbox graphic there, I think it was on the boss. Either that or fixed place.
About the 'how did they find another way to get to the moon' question, I have another theory. Even though ZUN said to ignore PC98 stuff when talking about canon Gensokyo (Something like that) , the last times the 'Dream World' was mentioned in Touhou was SoEW stage 3 , and LLS stages 3 to 6 and its Extra stage. If anyone remembers what Yuuka says to Reimu in the final stage, that was something like 'In a few hours you'll become a mist of atoms' (I know, it's not really precise) , meaning that the dream world, by itself, is quite hazardous, at least to Humans. Probably it did exist, but it clearly wasn't the preferred method of getting to the moon.