The paper presents a specification technique borrowing features from an formal and a semi-formal methods each in order to cover all features needed in the development of real-time and critical systems. The work is a contribution to the integration of formal and semi-formal methodsn namely STATEMATE and the temporal logic FNLOG [7]. FNLOG deals with quantitative temporal properties and is compatible with STATEMATE. The proposed integration approach uses the notations of STATEMATE and FNLOG, defines a various transformations rules of a STATEMATE specification towards FNLOG and extends the axiomatic of the temporal logic FNLOG by new lemmas to deal with duration properties. The paper presents the various steps of our integration approach.