.NET domain names are handled the same way as .COM domain names since in the same registry, so you can refer to answers about .COM too.
Your days calculation are ok, however you can not predict the precise time down to minute or even second because VeriSign does batch delete of domain names at some point during the day. Even if you knew when this process start, you have no idea how many domain names will be deleted then, in what orders, and how much time it takes to delete them. So you can at most do best guesses and have a solid idea on the day at least.
Note that even if you had the exact delete timestamp even up to the millisecond level that does not bring you a lot: you can not interact with the registry directly yourself, you need to go through a registrar. What guarantee do you have that your registrar will execute the EPP domain:create command just exactly after the timestamp? Even if it may have recorded an order to execute for it, it may have other operations going on, and/or applying whatever kind of priorities so that your specific domain creation may only happen later on.
What's the best strategy to be the first to register?
You will probably not like my answer but after 20 years of experience in this industry I still think it is the one that makes more sense.
You need to remove the emotional aspect attached to the specific domain name you are tracking right now and just start about trying to register any other one, which is not registered yet. With the current amount of different TLDs I am sure you can find alternatives that enable you not to expect some specific name for which you might deploy time and energy, with just the risk of missing it.
Whatever the goal is about fetching this particular domain name, I am quite sure you can get the same goal or close enough with another name.
Because there are registrars specialized in these cases, where you can "back order" domain names that is pay upfront (sometimes refundable sometimes not) to have your order in a queue and then hope that the registrar will be able to send the command at the appropriate time in order to get it. But note that there may be multiple customers, even at the same registrar, that wants the same name. In which case it may either be given to the first one, or go into some sort of auctions. And of course multiple registrars are competing against each other. So, in short, there is no 100% guaranteed strategy here and all the time and money you could invest will never get you 100% (depending on the domain name itself of course, and the risk that it may appeal to other people than you, it is certainly not the same if it is like a family name with no other significant sense, or a generic word, or a brand name).
So, again, my recommendation: try to find the same name in another TLD or some slight variation of it, until you come to something not registered yet and just register it now, without having to wait on external processes and multiple actors, and without having to pay anything besides a one year registration cost.
