Going from desktop to mobile development, for example, isn’t a monumental task necessarily but if you’re spinning up on an entirely new framework, language, and even way of thinking (old devices, low connectivity, etc) I’m extremely skeptical that you could learn it to any appreciable degree in a week of real time, let alone work time.
Sure, it’s possible there are factors making this transition easier, and yes some of those mobile concerns apply to desktop as well, but to me this reeks of a few possible situations, none of which are good:
1) Bob is doing things without really understanding what he’s doing, perhaps literally following a guide to the letter without a shred of critical thought about what he’s doing.
2) Bob is working far beyond what he’s billing
3) You’ve over-hired by a fair amount and your technology is so simple that people can solve your business needs even in disparate contexts extremely easily. If your Android app is just a web view connecting to your site, for example, sure i can see that being simple enough to fix in a week.