Bash has a "loadable" sleep which supports fractional seconds:
$ cd bash-3.2.48/examples/loadables
$ make sleep && mv sleep sleep.so
$ enable -f sleep.so sleep
$ which sleep
$ builtin sleep
sleep: usage: sleep seconds[.fraction]
$ time (for f in `seq 1 10`; do sleep 0.1; done)
The downside is that it may not be provided with your bash binary, so you would need to compile it yourself, as shown (though on Solaris it would not necessarily be as simple as I have shown above).
If that's not suitable, the next easiest thing to do is build or obtain
sleep from GNU coreutils, this supports the required feature.
As a last resort you could use
perl (or any other scripting that you have to hand) with the caveat that initialising the interpreter may be comparable to the intended sleep time:
$ perl -e "select(undef,undef,undef,0.1);"
$ echo "after 100" | tclsh