How long is a piece of string?
They usually start flowering after 4 or 5 years but may take longer. Some species flower every year and some of the most important ones, like Yellow Box, may flower on a 5 year cycle. Flowering can be at any time of the year depending on the season, the prevailing conditions and the species. The flow can be anything from a 2 weeks to 2 months, again depending on the conditions, species etc. What variety to target? Since your location appears to be Texas I would have thought your selection might be a bit limited, you may have to take whatever you can get.