3.75 seconds is an odd way to define the length of a video.
Durations in video are generally measured in Hours (H), Minutes (M), Seconds (S) and Frames (F), time code is in the basic format HH:MM:SS:FF. As a result there is not a straight forward way to enter the number of seconds in a decimal format in AE.
Instead you need to determine what the frame rate of your video is and convert the fractional portion of the seconds into frames. So, for example, when you say 3.24 you are most likely referring to 03:24 meaning 3 seconds and 24 frames. On the next frame it advances to 4 seconds, which I’m guessing means you are working at 25 frames per second.
So .75 seconds or 3/4 of one second would be equal to 25 frames per second * 3/4 seconds = 18.75 frames. Unfortunately you cannot have a fractional frame (one frame is the smallest unit) so you either need to move to a different frame rate or choose the closest whole integer frame value.
One option is to leave the frame rate at 25 frames per second and make your video 3 seconds and 18 frames long (so that it fits just under the 3.75 limit).
Alternatively you could change to a frame rate that evenly divides into 3/4 (0.75) such as 24 frames per second (24 * 3/4 = 18) or 60 frames per second (60 * 3/4 = 45). Personally I’d go with 24 if there are no frame rate requirements as there will be fewer frames to render (it will render faster than 60 frames per second).
Darby Edelen