At first, we introduce a unifying mathematical framework for many existing constraint-based approaches within systems biology and exemplify how it captures established resource allocation-type methods like resource balance analysis and dynamic enzyme-cost FBA. We then introduce time-optimal adaptation (TOA), a constraint-based modeling approach where the objective lies in reaching a pre-defined goal-state in as short time as possible. Mathematically, TOA falls into the problem class of time-optimal control problems. After shortly discussing some numerical details, TOA will be illustrated using a coarse-grained self-replicator model where we show that TOA can explain phenomena such as storage accumulation in microbes without taking competition and/or time-varying environments into account. The talk is based on a joint work with Alexander Bockmayr (TU Berlin) and Ralf Steuer (HU Berlin).