That is the perfect question to ask yourself before embarking on a screen scrape. If you have never built a screenscrape before, figure a little longer. For myself to do a good one, that output typed-data that I knew was reliable. I'd figure for a couple hours. 2 if things go smooth. 4 if they don't. Plus actual pull-time.
A final consideration when screen-scraping is to read terms and conditions of a site (if there are any) and make sure it's not a violation. You should also consider putting a throttler on it to prevent you hitting them with too much load too fast. A polite scraper will also read through the robots.txt file and comply. This site has one here: http://mentalhealth.samhsa.gov/robots.txt

Web scraping is a very common task, and VBA isn't always the fastest/best tool for it. It's doable, but seeing as how it is a government site/service you might just email them and ask if they can provide a full file. You'd be suprised how often that works.