What I said about only taking 10 mins was refactoring your @Mod annotation
I’ll break down the times (that I think it would take, from my Modding experience):
Refactoring @Mod annotation to META.INF file: 5-10 minutes (5 mins for basic mods, 10 mins for mods with dependencies)
Rewriting .lang to .json: 5 mins (10 mins if you do it all by hand, 2 mins if you use a tool to do it, 15 secs if your already prepared for it)
Flattening & removing getStateFromMeta & getMetaFromState: about 10 mins per block (5min for simple blocks with variants stored in meta, 10 mins for blocks with multiple types & variants stored in meta, already done ✅ if you prepared for it)
Changing OreDictionary to the Tag System: about 2 minutes per OreDictionary entry
Updating texture references (“/blocks/“ to “/block/“): 5 mins (15 seconds for a well written mod, 5min for a badly written one, 15min for a horribly written one)
Updating model variants (“normal” to “”): 10 mins (15sec for a well written mod, 10 for a badly written one, 15 for a horribly written one)
Moving data from /assets/ to /data/: 1min
Rewriting mod functionality: between 0 and infinite minutes, it depends 100% on what the mod did - some devs may not have to do anything, some may have so much work that they give up and never work on the mod again. Some mods may also not be necessary anymore.
I’ve prepared for 1.13 in my mod, and it should take me less that half an hour to fully update it for 1.12.2 to 1.13, every other Modder should be (and most are) preparing the same way.
ALL THESE NUMBERS ARE ESTIMATES BASED ON EXPERIENCE AND VERY FEW ACTUAL FACTS!
As Lex said