Real-time programmers have to deal with the problem of relating timing constraints associated with source code to sequences of machine instructions. This paper describes an environment to assist users in the specification and analysis of timing constraints. A timing analyzer predicts the best and worst case bounds for these constrained portions of code. A user interface for this timing analyzer was developed to depict whether these constraints were violated or met. A user is allowed to specify timing constraints within the source code of a C program. The user interface also provides three different methods for interactively selecting portions of programs. After each selection the corresponding bounded times, source code lines, and machine instructions are automatically displayed. Users are prevented from only selecting portions of the program for which timing bounds cannot be obtained. In addition, a technique is presented that allows the timing analysis to scale efficiently with complex functions and loops. The result is a user-friendly environment that supports the user specification and analysis of timing constraints at a high (source code) level and retains the accuracy of low (machine code) level analysis.