Frametime

gpGlobals->frametime

Time spent on last server or client frame. This is ideal for calculating progress per frame where it is unknown how many frames it should take.

Example

#define ALPHA_FREQUENCY 255 / 1.0f // Alpha should reach 255 in 1 second.

int alpha = 0;

void Think()
{
	alpha += ALPHA_FREQUENCY * gpGlobals->frametime;
}