works for me. thanks.

If timing as important (as in actual length) then the drop-frame timeline is more accurate.

So you're saying that my current Win 10 PC will have the length of a video I render different then what Vegas says if I do NOT use drop frame in the timeline?

Drop frame is used because there is not 30 frames in a second in TV. if you use non-drop (which pretends that there is 30fps), it will be 3 seconds off over an hour. If timing is critical, you need to use drop-frame. It does not affect the length of the video, only the REPORTED length. For a test, put a marker at 1 hr on your timeline and switch between drop and non-drop. (the best analogy is leap year. If we didn't have leap year, we would be off a day every four years.)

So it only matters if we're using media designed specifically for tv/broadcast playback (DVD/BD/etc.), or do digital electronic devices use drop frame in reporting length (tablets, PC media players, etc)?

I know the history and why, I'm asking about digital devices only, not complying to broadcast/NTSC specs or hardware.

AFAIK no media device uses timecode. They all have internal timers.

Courtesy Wikipedia

Drop frame timecode

Drop frame timecode originates from a compromise invented when color NTSC video was invented. The NTSC designers wanted to retain compatibility with existing monochrome televisions. To minimise subcarrier visibility on a monochrome receiver it was necessary to make the color subcarrier an odd multiple of half the line scan frequency; the multiple originally chosen was 495. With a 30 Hz frame rate the line scan frequency is (30 × 525) = 15750 Hz. So the subcarrier frequency would have been (495/2 × 15750) = 3.898125 MHz. This was the subcarrier frequency originally chosen, but tests showed that on some monochrome receivers an interference pattern caused by the beat between the color subcarrier and the 4.5 MHz sound intercarrier could be seen. The visibility of this pattern could be greatly reduced by lowering the subcarrier frequency multiple to 455 (thus increasing the beat frequency from approx 600 kHz to approx 920 kHz) and by making the beat frequency also equal to an odd multiple of half the line scan frequency. This latter change could have been achieved by raising the sound intercarrier by 0.1% to 4.5045 MHz, but the designers, concerned that this might cause problems with some existing receivers, decided instead to reduce the color subcarrier frequency, and thus both the line scan frequency and the frame rate, by 0.1% instead. Thus the NTSC color subcarrier ended up as 3.57954545 MHz (exactly 315/88 MHz), the line scan frequency as 15734.27 Hz (exactly 9/572 MHz) and the frame rate 29.97 Hz (exactly 30/1.001 Hz).[1]

This meant that an "hour of timecode" at a nominal frame rate of 30 frame/s, when played back at 29.97 frame/s was longer than an hour of wall-clock time by 3.6 seconds, leading to an error of almost a minute and a half over a day.

To correct this, drop frame SMPTE timecode was invented. In spite of what the name implies, no video frames are dropped (skipped) using drop-frame timecode. Rather, some of the timecodes are dropped. In order to make an hour of timecode match an hour on the clock, drop-frame timecode skips frame numbers 0 and 1 of the first second of every minute, except when the number of minutes is divisible by ten (i.e. when minutes mod 10 equals zero). (Because editors making cuts must be aware of the difference in color subcarrier phase between even and odd frames, it is helpful to skip pairs of frame numbers.) This achieves an "easy-to-track" drop frame rate of 18 frames each ten minutes (18,000 frames @ 30 frame/s) and almost perfectly compensates for the difference in rate, leaving a residual timing error of only 1.0 ppm, roughly 2.6 frames (86.4 milliseconds) per day.

That is, drop frame TC drops 18/18000 frame numbers, equivalent to 1/1000, achieving 30×0.999 = 29.97 frame/s. This is very slightly slower than the true NTSC frame rate of 30/1.001 = 29.97002997 frame/s, which is equivalent to dropping 1/1001 frame numbers. The difference is one additional NTSC frame per 1,000,000 drop frame TC values, which is negligible.

For example, the sequence when frame counts are dropped:
01:08:59:28
01:08:59:29
01:09:00:02
01:09:00:03

For each tenth minute
01:09:59:28
01:09:59:29
01:10:00:00
01:10:00:01

While non-drop timecode is displayed with colons separating the digit pairs—"HH:MM:SS:FF"—drop frame is usually represented with a semi-colon (;) or period (.) as the divider between all the digit pairs—"HH;MM;SS;FF", "HH.MM.SS.FF"—or just between the seconds and frames—"HH:MM:SS;FF" or "HH:MM:SS.FF". The period is usually used on VTRs and other devices that don't have the ability to display a semi-colon.

Drop frame timecode is typically abbreviated as DF and non-drop as NDF.