The 7941/61 phones are Java based and use use the time off the router, but they apply an offset based on the timezone configured under the CME.

Under telephony-service, add the correct time zone -

CME-Switch(config-telephony)#time-zone ?

<1-53> select timezone name used by IP phones (offset in minutes)

1 Dateline Standard Time -720

2 Samoa Standard Time -660

3 Hawaiian Standard Time -600

4 Alaskan Standard/Daylight Time -540

5 Pacific Standard/Daylight Time -480

6 Mountain Standard/Daylight Time -420

7 US Mountain Standard Time -420

8 Central Standard/Daylight Time -360

9 Mexico Standard/Daylight Time -360

10 Canada Central Standard Time -360

11 SA Pacific Standard Time -300

12 Eastern Standard/Daylight Time -300

13 US Eastern Standard Time -300

14 Atlantic Standard/Daylight Time -240

15 SA Western Standard Time -240

16 Newfoundland Standard/Daylight Time -210

17 South America Standard/Daylight Time -180

18 SA Eastern Standard Time -180

19 Mid-Atlantic Standard/Daylight Time -120

20 Azores Standard/Daylight Time -60

21 GMT Standard/Daylight Time +0

22 Greenwich Standard Time +0

23 W. Europe Standard/Daylight Time +60

24 GTB Standard/Daylight Time +60

25 Egypt Standard/Daylight Time +60

26 E. Europe Standard/Daylight Time +60

27 Romance Standard/Daylight Time +120

28 Central Europe Standard/Daylight Time +120

29 South Africa Standard Time +120

30 Jerusalem Standard/Daylight Time +120

31 Saudi Arabia Standard Time +180

32 Russian Standard/Daylight Time +180

33 Iran Standard/Daylight Time +210

34 Caucasus Standard/Daylight Time +240

35 Arabian Standard Time +240

36 Afghanistan Standard Time +270

37 West Asia Standard Time +300

38 Ekaterinburg Standard Time +300

39 India Standard Time +330

40 Central Asia Standard Time +360

41 SE Asia Standard Time +420

42 China Standard/Daylight Time +480

43 Taipei Standard Time +480

44 Tokyo Standard Time +540

45 Cen. Australia Standard/Daylight Time +570

46 AUS Central Standard Time +570

47 E. Australia Standard Time +600

48 AUS Eastern Standard/Daylight Time +600

49 West Pacific Standard Time +600

50 Tasmania Standard/Daylight Time +600

51 Central Pacific Standard Time +660

52 Fiji Standard Time +720

53 New Zealand Standard/Daylight Time +720

If you are EST, then this would be -300, so select option 12.

You then need to use the 'create cnf' command to rebuild all the XML config files for the phones. Reset the handsets and after they re-register the time should be correct.