It's not "meant to be creatable in a day." There's just in a very broad category with a hard floor that "it won't take you less than a day." It's meant
to be created when the combination of your coin production by crafting + coin committed from appropriate materials equals at least its value of 50s
. The default is you can use raw materials up to half the value (or put another way you can match crafted value with materials value 1:1).
With no Crafting Feat and a downtime roll result of 16-25 you'd need to have had at least 9 days of downtime (27 silver) and 23 silver of mats to make up the remainder. Actually an uninterrupted week is sufficient to too, since a week with a roll of 16-25 produces 30s (then just add 20s of materials).
With Crafting Basics and a downtime roll result of 16-25 you'd need to have had at least 5 days of downtime (30 silver) and 20 silver of mats to make up the remainder.
With Crafting Mastery and a downtime roll result of 16-25 you'd need to have had at least 2 days of downtime (36 silver) and 14 silver of mats to make up the remainder (note: you could make something with a value of 48 silver in 1 day since you've produced 18s, and could use up to twice that in mats with this feat- that extra 2 silver for you potion is what tips it into a second day and you make another 18 silver anyway, so no need to use so many mats).