Dashboard is designed to see current activities on your MySQL and SSH server. It helps you to quickly look at charts and analyze recent activities on server.
However you can get chart upto last 200 data collections (If default data collection is given i.e. 5 mins, You can see chart generated for last 16 hours)
Further you want to see historical data you can get it using History/Trend report of Monitors page wherein you can get details about particular counter for last #hours,days,Months,Years and Custom timeframe as well.