It doesn't matter when you dose, no. Nutirent levels will begin to accumulate as you dose - the whole point of estimative index is ensuring nutrient levels don't become limited by dosing a bit more than is needed - an "estimated" amount. Therefore, you can dose any time, day or night...you can even miss a day (if you're on vacation or something) and won't see any major problems as a result, but I wouldn't recommend it as a normal course of action (ie don't get lazy).
I've had weeks that I've been so busy I can't make the water change; when this happens, I will usually continue to dose, though at lower concentrations (it's not at all an exact science - hence the "estimative" part)...I just sort of "guess" what I can add without causing problems. so far, so good.
That said, the weekly water change is imperative...50% minimum ensures nutrient levels are "reset" and do not accumulate in excess. It's good, especially early on while you're really motivated, to keep a really rigid schedule: dose daily and do your weekly water changes. Once you get that hang of it, you'll see that it's not that complicated. The key with an EI tank is personal discipline.
Also, I noticed your thread was titled "IE...." instead of "EI (for estimative index)..." You might get more responses if you correct it, though I'm sure most people get what you're trying to say....