Most modern uses of phylogenetic trees require chronograms: trees with branch lengths proportional to time. There are many challenges to making these, and further challenges to using them. This talk will cover two main avenues for this. The first is developing practical ways to enable reuse of existing knowledge, including ways to aggregate information from shared chronograms and ways to make techniques usable via R packages and web interfaces. The second is the importance of incorporating the biasing effect of uncertainty in estimating chronograms and in using them.