The time it takes to download a podcast to your Apple Watch depends on several factors including the size of the podcast, the speed of your internet connection, and how busy Apple's servers are at the time.

However, as a general guide, most podcasts should take anywhere from a few seconds to a few minutes to download. If you are downloading multiple episodes or an entire series, it could take longer.

Here's how you can do it:

1. Open the Apple Watch app on your iPhone.
2. Tap 'My Watch', then tap 'Podcasts'.
3. Choose how you want to add podcasts:
- Listen Now: Episodes from shows you subscribe to or listen to most will automatically sync to your Apple Watch.
- Custom: Choose which shows to sync, and limit the number of episodes that sync to your Apple Watch.
4. Now, connect your Apple Watch to Wi-Fi and place it on its charger. The sync process will start automatically.

Remember, your Apple Watch must be charging in order to sync podcasts.