Something along the lines of:

print $target = time + 10; 
print $s and sleep $s while ( $s = ($target - time )/2 ) > 0; 
print time;;
1203221999.59375
5
2.49999403953552
1.24999451637268
0.624994039535522
0.312494516372681
0.15625
0.0781184434890747
0.0390595197677612
0.0155709981918335
0.00779902935028076
1203221999.59376
[download]

would work quite well. If the "do something" might take longer than half the delay time, then use a larger divisor:

print $target = time + 10; 
print $s and sleep $s while ( $s = ($target - time )/3 ) > 0; 
print time;;
1203222233.07813
3.33329796791077
2.21874562899272
1.47916666666667
0.984371026357015
0.656246026357015
0.437496026357015
0.29166833559672
0.192704677581787
0.125013987223307
0.0833380222320557
0.0520946979522705
0.0311883290608724
0.0208296775817871
0.010399341583252
0.0052033265431722
1.98682149251302e-006
1203222233.07822

print $target = time + 10; 
print $s and sleep $s while ( $s = ($target - time )/4 ) > 0; 
print time;;
1203222257.71875
2.4999732375145
1.87499701976776
1.40624725818634
1.05468475818634
0.78905975818634
0.58984100818634
0.44140350818634
0.328112483024597
0.246071517467499
0.183622241020203
0.136751472949982
0.10155975818634
0.0742244720458984
0.0546977519989014
0.0386837720870972
0.0273575186729431
0.0195417404174805
0.011723518371582
0.00780248641967773
0.00391250848770142
1.59740447998047e-005
1203222257.71881
[download]