Explicitly convert float to int for startTimer

[stanislavlevin]

As of Python3.10:

Builtin and extension functions that take integer arguments no longer
accept Decimals, Fractions and other objects that can be converted to
integers only with a loss (e.g. that have the int() method but do not
have the index() method). (Contributed by Serhiy Storchaka in
bpo-37999.)

startTimer accepts only integers (milliseconds) and fails to
implicitly convert floats.

Fixes: #128