The following is a variation on Heike's answer allowing different colors and durations for different graphics objects:

    ClearAll[signal1];
    signal1[dta_, duration_, color_][t_] := 
     Piecewise[{{{Lighter[color, (t - dta[[-1]])/duration], Disk[dta[[{3, 2}]], dta[[5]]/10]},  dta[[-1]] <= t < dta[[-1]] + duration}, 
      {{},  t < dta[[-1]] || dta[[-1]] + duration <= t}}]; 
    With[{tmin = AbsoluteTime[{2012, 3, 19, 23, 0}],  
          tmax = AbsoluteTime[{2012, 3, 20, 0, 0}]},
    frames = Table[ Graphics[{{White, Rectangle[{10, 43}, {13, 46}]}, 
     Text[Style[ DateString[  t, {"Day", " ", "MonthNameShort", " ", "Year", " ", "Hour", 
         ":", "Minute"}], FontFamily -> "Helvetica", FontSize -> 20], {10.8, 45.85}], 
    MapThread[{signal1[#1, #2, #3][t]} &, {data, {3600, 2400, 
        900}, {Red, Green, Blue}}]}], {t, tmin, tmax, 60}]];
    Export["fadingdisks1.gif", frames, "DisplayDurations" -> .03]

![enter image description here][1]

Another variation that ties the disk radii to time:

    ClearAll[signal2b];
    signal2b[dta_, duration_, color_][t_] := 
     Switch[dta[[-1]] <= t < dta[[-1]] + duration,  
       True, {Lighter[color, (t - dta[[-1]])/duration], 
             Disk[dta[[{3, 2}]], (1 - (t - dta[[-1]])/duration) dta[[5]]/ 10]}, 
       _, {}]; 
    With[{tmin = AbsoluteTime[{2012, 3, 19, 23, 0}], 
          tmax = AbsoluteTime[{2012, 3, 20, 0, 0}]}, 
    frames = Table[
     Graphics[{{White, Rectangle[{10, 43}, {13, 46}]}, 
       Text[Style[DateString[ t, {"Day", " ", "MonthNameShort", " ", "Year", " ", "Hour", 
         ":", "Minute"}], FontFamily -> "Helvetica", FontSize -> 20], {10.8, 45.85}], 
    MapThread[{signal2b[#1, #2, #3][t]} &, {data, {3600, 2400, 
        600}, {Red, Green, Blue}}]}], {t, tmin, tmax, 60}]];
    Export["fadingdisks2b.gif", frames, "DisplayDurations" -> .03]

![enter image description here][2]

Note: You can also use `{color, Opacity[1 - (t - data[[-1]])/duration],...}` instead of `{Lighter[color, (t - data[[-1]])/duration},...}` in definitions of `signal1` and `signal2b`.


  [1]: https://i.sstatic.net/aG8mb.gif
  [2]: https://i.sstatic.net/fLsul.gif