Google Play may be getting a "Refresh" button for updates in the near future8
If getting notifications about seeded updates is not good enough for you, as they may come in an hour or two later, you may soon be able to check for app updates manually. This will be a neat addition to the current “My apps & games” section, which lists available updates for your installed apps, and will let you refresh the page without having to close and re-open Google Play.
The feature is currently being tested and is not widely available, but will likely reach you in a month or two's time, as is usual with beta features on Android. The update will also bring a couple of other changes to the Play Store UI, among which is the option to sort your installed apps and games by various criteria, such as name, size, last updated, and last used.