No, when you join two electromagnetic waves with equal frequencies but with one being delayed, the resultant wave will still have the same frequency as the original waves. The delay will affect the phase of the wave, but it will not change the frequency.
In electromagnetic wave terminology, the frequency refers to the number of complete cycles the wave undergoes in a given unit of time. Delaying one wave with respect to the other will introduce a phase shift, meaning the peaks and troughs of the waves will not align perfectly. This phase shift may cause constructive or destructive interference, resulting in a varying amplitude (strength) of the combined wave at different points in time.
However, the frequency of the wave remains unchanged. The frequency is determined by the source that generates the wave and does not depend on phase shifts or delays.