Hi – for search twitter allows ‘180 requests/queries per 15 minutes’. A ‘query’ for TAGS returns 100 tweets.
TAGS is also limited by quotas imposed by Google, which I’m guessing are the ones you are hitting. For a ‘consumer’ account (gmail.com) you can have 20,000 queries a day (a lot more if you are Edu or Gov user). There are also limits on the amount of server time you can use – harder to measure. If you are hitting Google limits one way around this is using multiple Google accounts.