I remember reading somewhere that a bard (of doom?) could take the place of a space or time player due to their ability to mimic other aspects. Of course, I'm pretty sure you need a space player's land to get frogs and a time player's land to perform the scratch. So my question is that do you think a bard could temporary replace an absence space/time player? (Whether they be dead or just missing?) And if so, to what extent and how long?

I don’t think a Bard could fill in for the position of an Aspect that is not theirs. Aspects are something intrinsically tied to the nature of the Players as people. Emulating other Aspects other than your own tends to be pretty damaging and not end up well.