Without wishing to complicate matters, the reason that you ideally need to keep track of the number of gains is that using an alacrity you are almost certainly going to cross the various ROT thresholds at some point.
If you start at 70 (which you should only do if you have more than one alacrity available) then 29 gains will on average take you up to 80. That represents 29/50 or 58% of your daily gains, assuming you are gaining in no other skill, meaning you have 42% of 40 or 16-17 gains left at 8 minute intervals, which should get you to just over 85 on that first day of using the scroll. Keeping track of the gains means that you are not wasting time trying to get a gain once your daily allowance is at an end.
So, at the end of the first day you will have made around 45 gains. If we assume an average of 15 seconds per gain (log in, get gain, log out) then you will still have another 15 gains available the next day before the scroll is finished. However, the time it takes between gains will vary considerably between skills. With some crafting skills you can probably get down to around ten seconds.
But with a skill like peacing you really need to set things up for the character making the gains if you want to get the maximum advantage from the scroll. If you are using the scroll and then gating from your log-out spot, trying to find a creature and the gating back, you will not get many gains for your money.
What you need to do is use a tamer character to bring a suitable animal to your house and release it (although it is technically illegal to keep wild animals caged inside a 'pen' though). Then you set up a macro (use peace/last target) and you can log in, get your gain (possibly requiring more than one attempt), and log out quickly. You want to be hitting the 'log out' button/key as soon as you are in and then hit the conformation once you see that you have your gain.
The best alacrity I had was when I took vet from 82 to over 110 by using one tamer to get a cu beaten up in Destard and then bringing it back to a house and getting it to stay at the spot next to where the alacrity tamer would appear. Once I had the gain I would log out with the cu tamer too and so could make 3-5 gains before needing to get the pet damaged again. I use multiple computers, but you could still do it with one if the first tamer was not friended to the house and so would not instantly log out.
When trying to decide what pets are needed for bard gains,
try this.