There has been a debate in Tunisia and Egypt on when elections should be held. In Tunisia, the electoral commission itself suggested that the July 24 elections should be postponed till October, although the interim government has refused to budge. In Egypt, the debate started immediately about when the referendum should be held, although these were ignored, and some persist in asking more time before parliamentary elections are held (they were already postponed from June to September). On both sides of the argument, people have many reasons. Some seem entirely valid to me, and others much less so.
The first reason for postponement is often that early elections will lead to the return of elements of the previous regime. I can understand the worry, but in Tunisia and Egypt, where the ruling parties were dissolved, I don't think there is much of a chance of that happening. The RCD and NDP have been stripped of their assets and are thoroughly discredited. Tunisia went further and barred RCD members for running (Egypt has yet to do something similar, and probably won't.) Some of the same people (notably in the countryside) will be elected under a different party name or as independents, for sure, but a wholesale replacement of the political class was always unrealistic. I'm not too worried about it.
The second reason is because early elections give the advantage to Islamists. Again, I don't think it's a very good reason, and that three months or so won't make a difference. Furthermore, changing the dates on the ground that they benefit a particular party seems plainly wrong to me, particularly as there is an actual urgency is restoring parliament so that it can pass laws, etc. Otherwise you continue to have weak transitional governments (Tunisia and Egypt) and/or military rule (Egypt). Islamists will do much better than they have in the past, the question seems to me to be how to ensure that they operate within a national democratic consensus: i.e. no right to participate in elections unless there is an adherence to common principles: equality for all under the law, rotation of power, etc. Only extreme Islamists like Salafists would be denied the right to participate under such procedures. Tunisia is already doing a better job at that, despite rumors of a coup in the case of a Nahda victory (that would obviously be a disaster).
The third reason is about ensuring a reform of the electoral system before the election. This seems to me to be the most valid reason of them all. Egypt's referendum was held under a system in which it was impossible to ensure that people did not vote twice — staining thumbs with ink simply is not enough. Not enough is being done in both countries to ensure the electoral procedures are beyond reproach, and in Egypt there is too little consultation and transparency on the forthcoming electoral law. The governments of Egypt and Tunisia should be spending much of its time to make sure Egypt has the cleanest, most irreproachable election in its history. Tunisia is off to a better start — both in terms of political consensus and governance — but the incompetent management of the transition by the SCAF (as Sandmonkey points out) puts Egypt is a more uncertain place. We can't let the perfect be the enemy of the good in the first post-revolution elections in the Arab world, but we have to at least get to good enough. I'm not sure things are there yet.