If an SSR accepts an analog input, the literature will tell you the time duration. It might be something like one of these:
1) 4-20mA analog input, burst firing: "Overall cycle time = 0.5 seconds. Example: 12 mA = 50% = 0.25 seconds ON, 0.25 OFF, 0.25 ON, 0.25 OFF."
2) 4-20mA analog input, phase angle: "Delayed turn ON inside the sine wave. 8 mA = 25% = delayed start until 25% into the sine wave, then ON until the zero mark, delay 25%, then ON until the zero mark, etc"
3) 0-10 V analog input, half sine wave burst firing. 3.3 Volt = 33% = half a sine wave ON, then 2 half sine waves OFF.
Options 1 and 3 above are zero crossing so they are electrically noise free. Option 2 is phase angle. It provides very good control but generates electronic noise that may be an issue especially in CE installations in Europe. Phase angle is typical for transformer coupled loads. Zero crossing is typical for resistive loads (most heaters). The half sine wave burst firing is for very fast loads such as IR heaters, etc.