[latchkey]

Development time isn't slower when you factor in all the bugs it saves you from dealing with down the road when you're either wonder what is the type of an object or why something isn't working during runtime that a compiler could have caught.

[a_wild_dandan]

Also, if you're working with an untyped APIs, define the types you're using. It doesn't have to be complete or perfect. But having that formal contract will save you time and make explicit your assumptions. In the best case, you can contribute those types to the API to everyone's benefit.