at intervals
at irregular intervals
at random
at regular intervals
at stated times
brokenly
by catches
by fits
by jerks
by skips
by snatches
capriciously
constantly
desultorily
disconnectedly
discontinuously
eccentrically
erratically
every so often
fitfully
haltingly
haphazardly
here and there
in snatches
in spots
inconstantly
infrequently
intermittingly
irregularly
jerkily
like clockwork
lurchingly
methodically
nonuniformly
occasionally
off and on
patchily
per saltum
punctually
randomly
regularly
roughly
skippingly
spasmodically
sporadically
spottily
steadily
systematically
uncertainly
unevenly
intermittence
intermittent
concomitantly