In this case, the best strategy would be to see if you can adjust your work schedule. If there is no way to change it, you would need to delay your immersion to Friday night.
Tevilah during the day is only permitted from the eighth day onward in cases where
tevilah at night is not possible. Even when daytime immersion is permitted, it is customary for the woman to return home only after nightfall. Thus, in your case, Friday night
tevilah is the most appropriate course of action.
Note that
tevilah is permitted at any time during the night, until
alot hashachar (halachic dawn). If you can find another woman who works shifts, or who wakes up very early, you might be able to arrange to immerse in the mikveh before a
lot hashachar, at the end of the night.
