Hello Max,.
welcome here at the Amorphophllus crazy...
a small challenge is titanum not necessarily soooo hard, but as the first Amorphophallus.
There are also different origins and I have the feeling, that you are different difficult or -growing according to some - that is more intuitive...
On duration, perlite as inert and not pufferndes substrate is may not be as cheap, especially because it is so very wet immediately after pouring. There are possibly more favourable Seramis, pumice gravel or Vulcaponic.
Titanum cultivate many but also in peat-based substrates under admixture of 30 - 50% perlite.
Fertilize you have to quite a while sure until after the Blat is unfolded. the thick seed has quite a few nutrients for the first time to offer. But a light fertilization hurt soon after the Bltt is deployed does not. Well fed titanum have a really dark green leaves...
It is important in titanum, still, that the tuber in the rest period in
light should remain damp substrate. a better expression might be damp. This prevents that dehydrates the tuber.
Next to it is titanum wärembedürftig, also in the rest period! There, but also ZImmertemperaturen rich... so at best 20 ° C...
(many species here:
Amorphophallus soil/dormancy list / substrate / storage conditions / rest period )
Otherwise check this here:
Culture guide of Amorphophallus titanum
Seramis as Subtrat for difficult species (titanum, gigas, decus-silvae etc.)
A. titanum and the light...
You take what Earth
Happy growing, Bernhard.