How to make permanent ink that appears after some time?
Depending on what you want to do (what do you want to do?) you might be looking for gall ink.  Briefly, the chemistry works like this: the recipe consists of soluble polyphenols (typically gallic acid) and a Fe(II) salt.  The preparation must be stored in an air-tight container and even then decomposes over time.  As soon as it is applied to paper and exposed to air, the Fe(II) is oxidized to Fe(III), which forms insoluble deeply coloured complexes with your polyphenol.  The permanent colour takes about a day to develop.  That's why often a non-permanent dye is added so people can see what they are writing.