I do not think there is an absolutely right or wrong answer, as the appropriate amount of time to invest in any individual application will depend on a multitude of factors such as:
- Your research and application writing speed: depending on how much prior experience you have had with researching firms and writing applications, and depending on how much time and effort you have invested in honing those research and writing skills to perfection, you may be able to complete applications to a high standard significantly faster/slower than other people.
- Your goals and applications strategy: if you are planning on applying to another 20-30 more firms before the end of the cycle or are planning to only apply to another 5-10 should also play an important role in how you apportion your efforts - the more applications you aim to complete, the less time you should aim to spend on every single application.
- The specific firm and its application form: some firms are a lot easier to apply to than others - because they ask you fewer questions, because the questions are easier/more standard, because the firm is easier to research and to connect motivations to, etc.
- Your other commitments: if you are employed, studying, or have other significant commitments taking up substantial amounts of your time, once again, that will influence the total amount of time you can invest in writing applications during the next period. This in turn should influence how much time you should feel happy with taking to complete any given application.
In my case, the most significant factor by far was the first one - as at the beginning of my last applications cycle, it was taking me 1-2 weeks to write a high-quality application, while by the end, it was taking me around half a day (maybe 5-6 hours of focused work). I would advise you to determine how much time you want to spend on average per firm by simply dividing the number of applications you want to complete by the available time, and then make adjustments depending on the aforementioned factors.
Importantly, while writing your applications you should keep in mind that:
- You should not rush any application to the extent that the end product cannot be classified as objectively high-quality, as then all your good work will likely be in vain; and
- You should not aim for perfection: you do to need to redraft the same bits again and again and again only to obtain very marginal improvements. Instead, once you feel you have achieved a high level of quality, you should simply submit and move on to the next one.